APPENDIX A
SEISMIC-FORCE-RESISTING ELEMENTS
IN BUILDINGS
This handbook discusses techniques for rehabilitating the seismic resistance of the following 15 common building types: 
1.
Wood Light Frame 
2.
Wood, Commercial and Industrial 
3.
Steel Moment Frame 
4.
Steel Braced Frame 
5.
Steel Light Frame 
6.
Steel Frame with Concrete Shear Walls 
7.
Steel with Infill Masonry Shear Walls 
8.
Concrete Moment Frame 
9.
Concrete Shear Walls 
10.
Concrete Frame with Infill Walls 
11.
Precast/Tilt-Up Concrete Walls with Lightweight Flexible Diaphragm 
12.
Precast Concrete Frames with Concrete Shear Walls 
13.
Reinforced Masonry Bearing Walls with Wood/Metal Deck Diaphragms 14.
Reinforced Masonry Bearing Walls with Precast Concrete Diaphragms 15.
Unreinforced Masonry Bearing Wall Buildings The lateral-force-resisting elements of buildings can be categorized into the following subsystems: vertical elements resisting lateral forces, diaphragms, foundations, and the connections between the subsystems. The 15 common building types considered in this report can be composed of various subsystem types. The construction of each subsystem can vary. For example, diaphragms can be constructed of timber, steel or concrete. The technique to rehabilitate a deficient subsystem and hence a deficient building depends upon the type of construction of that subsystem. The following tables present common construction of the lateral-force-resisting subsystems for the 15 common building types. These tables are provided to aid the reader in determining the types of subsystems likely to be present in a building of a given type. With an understanding of the subsystem construction and the subsystem deficiencies, the techniques presented in Chapter 3 can be investigated to determine effective ways to rehabilitate the seismic resistance of a given existing building.
149 
TABLE Al STRUCTURAL ELEMENTS OF COMMON BUILDING TYPE 1--WOOD, LIGHT FRAME Floor Roof Vertical-Resisting Diaphragm Elements Foundations Connections Timber framing with Wood stud walls with Spread footings, piles, Diagonal wire or strut plywood, straight-laid, let-in or cut-in timber or drilled piers. bracing of ceilings from or diagonal sheathing. bracing or plywood, floor roof diaphragms.
straight-laid, or diagonal sheathing. Bracing or lateral support of walls and partitions from ceilings or diaphragms.
Nailing and blocking for direct shear transfer from horizontal diaphragms to shear walls or vertical bracing.
Drag struts to collect shear from horizontal diaphragms for transfer to shear walls or vertical bracing.
Bolting of shear walls and vertical bracing to concrete slabs or foundation walls.
Tension ties or hold-downs for shear walls and vertical bracing.
Nailing or bolting of vertical bracing.
150 
TABLE A2 STRUCTURAL ELEMENTS OF COMMON BUILDING TYPE 2--WOOD, COMMERCIAL AND INDUSTRIAL Floor Roof Vertical-Resisting Diaphragm Elements Foundations Connections Timber framing with Wood stud walls with Spread footings, piles, Diagonal wire or strut, straight-laid, let-in or cut-in timber or drilled piers. of ceilings from floor diagonal sheathing. bracing or plywood, roof diaphragms.
(Floor roof deck- straight-laid, or may be 2-inch sheathing. Bracing or lateral support of material). walls and partitions from Knee bracing or ceilings or diaphragms.
bracing of timber columns. Nailing and blocking for direct shear transfer from horizontal diaphragms to shear walls or vertical bracing.
Drag struts to collect shear from horizontal diaphragms for transfer to shear walls or vertical bracing.
Bolting of shear walls and vertical bracing to concrete slabs or foundation walls.
Tension ties or hold-downs for shear walls and vertical bracing.
Nailing or bolting of vertical bracing.
151 
TABLE A3 STRUCTURAL ELEMENTS OF COMMON BUILDING TYPE 3--STEEL MOMENT FRAME Floor Roof Vertical-Resisting Diaphragm Elements Foundations Connections Timber framing with Moment resisting
* Spread footings, piles, Diagonal wire or strut, straight-laid, structural steel frames. or drilled piers of ceilings from floor diagonal sheathing. roof diaphragms.
Reinforced concrete Bracing or lateral support of slab supported on walls and partitions from structural steel floor ceilings or diaphragms.
framing members.
Nailing and blocking for 
Steel decking with or shear transfer from without concrete fill. horizontal diaphragms to shear walls or vertical bracing.
Drag struts to collect shear from horizontal diaphragms for transfer to shear walls or vertical bracing.
Shear studs or other connections of concrete diaphragm to steel chord members.
Welding, shear studs, or other connections of steel deck diaphragms to structural steel framing.
Splice detail of steel chord members.
Beam/column connections.
Beam/column panel joint details.
Column splice details.
Column base details.
152 
TABLE A4 STRUCTURAL ELEMENTS OF COMMON BUILDING TYPE 4--STEEL BRACED FRAME Floor Roof Vertical-Resisting Diaphragm Elements Foundations Connections Timber framing with Concentric steel Spread footings, piles, Diagonal wire or strut, straight-laid, in diagonal, X, K, or drilled piers of ceilings from floor diagonal sheathing. or chevron diaphragms.
Reinforced concrete Bracing or lateral support of slab supported on May also have moment walls and partitions from structural steel floor resisting structural ceilings or diaphragms.
framing members. steel frames.
Nailing and blocking for Steel decking with or shear transfer from without concrete fill. horizontal diaphragms to shear walls or vertical bracing.
Drag struts to collect shear from horizontal diaphragms for transfer to shear walls or vertical bracing.
Shear studs or other connections of concrete diaphragm to steel chord members.
Welding, shear studs, or other connections of steel deck diaphragms to structural steel framing.
Splice detail of steel chord members.
Beam/column connections.
Beam/column panel joint details.
Column splice details.
Column base details.
Bolted or welded bracing connections.
153 
TABLE AS STRUCTURAL ELEMENTS OF COMMON BUILDING TYPE 5--STEEL, LIGHT FRAME Floor Roof Vertical-Resisting Diaphragm Timber framing with I Elements Moment resisting Foundations Spread footings, piles, Connections Diagonal wire or strut 
1 plywood, straight-laid, structural steel frames. or drilled piers of ceilings from floor diagonal sheathing. roof diaphragms.
Concentric light steel Reinforced concrete bracing in diagonal or Bracing or lateral support of slab supported on X configuration. walls and partitions from structural steel floor ceilings or diaphragms.
framing members.
Nailing and blocking for Steel decking with or shear transfer from without concrete fill. horizontal diaphragms to shear walls or vertical bracing.
Drag struts to collect shear from horizontal diaphragms for transfer to shear walls or vertical bracing.
Shear studs or other connections of concrete diaphragm to steel chord members.
Welding, shear studs, or other connections of steel deck diaphragms to structural steel framing.
Splice detail of steel chord members.
Beam/column connections.
Beam/column panel joint details.
Column splice details.
Column base details.
Bolted or welded bracing connections.
TABLE A6 STRUCTURAL ELEMENTS OF COMMON BUILDING TYPE 6--STEEL FRAME WITH CONCRETE
SHEAR WALLS Floor Roof Vertical-Resisting Diaphragm Elements Foundations 
Reinforced concrete Non-moment-resisting Spread footings, piles, slab supported on steel frames. or drilled piers.
structural steel floor framing members. Reinforced concrete shear walls.
Steel decking with or without concrete fill. May also have moment resisting structural steel frames.
Connections Diagonal wire or strut bracing of ceilings from floor roof diaphragms.
Bracing or lateral support of walls and partitions from ceilings or diaphragms.
Shear studs or other connections of concrete diaphragm to steel chord members.
Welding, shear studs, or other connections of steel deck diaphragms to structural steel framing.
Splice detail of steel chord members.
Beam/column connections.
Beam/column panel joint details.
Column splice details.
Column base details.
Connection of concrete shear walls to floor roof diaphragms.
Development of boundary members for concrete shear walls.
155
TABLE A7 STRUCTURAL ELEMENTS OF COMMON BUILDING TYPE 7--STEEL WITH INFILL MASONRY SHEAR WALLS Floor Roof Vertical-Resisting 1 Diaphragm Elements Foundations Connections Timber framing with Nonmoment-resisting Spread footings, piles, Diagonal wire or strut bracing plywood, straight-laid, steel frames. or drilled piers of ceilings from floor diagonal sheathing. roof diaphragms.
Unreinforced masonry Reinforced concrete walls. Bracing or lateral support of slab supported on walls and partitions from structural steel floor May also have moment ceilings or diaphragms.
framing members. resisting structural steel frames. Nailing and blocking for 
Steel decking with or direct shear transfer from without concrete fill. horizontal diaphragms to shear walls or vertical bracing.
Drag struts to collect shear from horizontal diaphragms for transfer to shear walls or vertical bracing.
Shear studs or other connections of concrete diaphragm to steel chord members.
Welding, shear studs, or other connections of steel deck diaphragms to structural steel framing.
Splice detail of steel chord members.
Beam/column connections.
Beam/column panel joint details.
Column splice details.
Column base details.
Connection of masonry walls to steel framing.
TABLE A& STRUCTURAL ELEMENTS OF COMMON BUILDING TYPE 8--CONCRETE MOMENT FRAME
Floor Roof Vertical-Resisting Diaphragm Elements Foundations Connections Reinforced concrete Reinforced concrete Spread footings, piles, Diagonal wire or strut bracing monolithic with frames. or drilled piers. of ceilings from floor reinforced concrete roof diaphragms.
beams and girders.
Bracing or lateral support of walls and partitions from ceilings or diaphragms.
Beam/column panel joint details.
Column shear reinforcement and confinement.
157 
TABLE A9 STRUCTURAL ELEMENTS OF COMMON BUILDING TYPE 9--CONCRETE SHEAR WALLS
Floor Roof Vertical-Resisting Diaphragm Elements Foundations Connections Reinforced concrete Reinforced concrete Spread footings, piles, Diagonal wire or strut bracing slab monolithic with shear walls. or drilled piers. of ceilings from floor reinforced concrete roof diaphragms.
beams and girders.
Bracing or lateral support of walls and partitions from ceilings or diaphragms.
Connection of concrete shear walls to floor roof diaphragms.
Development of boundary members for concrete shear walls.
Concrete diaphragm chord details.
158 
TABLE A10 STRUCTURAL ELEMENTS OF COMMON BUILDING TYPE 10--CONCRETE FRAME WITH INFILL WALLS Floor Roof Vertical-Resisting Diaphragm Elements Foundations Connections Timber framing with Reinforced concrete Spread footings, piles, Diagonal wire or strut plywood, straight-laid, frames. or drilled piers. bracing of ceilings from floor diagonal sheathing. roof diaphragms.
Unreinforced masonry Reinforced concrete walls. Bracing or lateral support of slab monolithic with walls and partitions from reinforced concrete ceilings or diaphragms beams and girders.
Connection of timber floor roof diaphragms to concrete frames.
Connection of concrete floor roof diaphragms to concrete frames.
Connection of masonry walls to concrete frames.
Beam/column joint details.
Column shear reinforcement and confinement.
159 
TABLE All STRUCTURAL ELEMENTS OF COMMON BUILDING TYPE 11--PRECAST/TILT-UP CONCRETE WALLS WITH LIGHTWEIGHT FLEXIBLE DIAPHRAGM Floor Roof Vertical-Resisting Diaphragm Elements Foundations Connections ] Timber framing with Precast concrete walls. Spread footings, piles, Diagonal wire or strut plywood, straight-laid, or drilled piers. bracing of ceilings from floor diagonal sheathing. roof diaphragms.
Reinforced concrete Bracing or lateral. support of slab monolithic with walls and partitions from reinforced concrete ceilings or diaphragms.
beams and girders.
Welding, shear studs, or Steel decking with or other connections of steel without concrete fill. deck diaphragms to structural steel framing.
Connection of timber floor roof diaphragms and precast walls.
Connection of concrete floor roof diaphragms to precast walls.
Connection of steel deck floor roof diaphragms to precast walls.
Vertical precast panel connections.
Tension ties or hold-down connections for precast panels.
Diaphragm chord details for timber, steel decking, and concrete diaphragm.
Base detail for precast panels.
160 
TABLE A12 STRUCTURAL ELEMENTS OF COMMON BUILDING TYPE 12--PRECAST CONCRETE FRAMES
WITH CONCRETE SHEAR WALLS Floor Roof Vertical-Resisting Diaphragm Elements Foundations Connections Reinforced concrete Precast concrete Spread footings, piles, Diagonal wire or strut slab monolithic with frames. or drilled piers. bracing of ceilings from floor reinforced concrete roof diaphragms.
beams and girders. Reinforced concrete shear walls. Bracing or lateral support of walls and partitions from ceilings or diaphragms.
Connection of concrete floor roof diaphragms to precast frames or shear walls.
Development of boundary members for concrete shear walls.
Beam/column joint details.
Column shear reinforcement and confinement.
Concrete frame splice details.
161 
TABLE A13 STRUCTURAL ELEMENTS OF COMMON BUILDING TYPE 13--REINFORCED MASONRY WALLS
WITH WOOD/METAL DECK Floor Roof Vertical-Resisting Diaphragm Elements Foundations Connections Timber framing with Unreinforced masonry Spread footings, piles, Diagonal wire or strut plywood, straight-laid, bearing walls. or drilled piers. bracing of ceilings from floor or diagonal sheathing. roof diaphragms.
Steel decking with or Bracing or lateral support of without concrete fill. walls and partitions from ceilings or diaphragms.
Welding, shear studs, or other connections of steel deck diaphragms to structural steel framing.
Connection of timber or steel decking floor roof diaphragms to masonry walls.
Tension ties or hold-downs for masonry walls.
162 
TABLE A14 STRUCTURAL ELEMENTS OF COMMON BUILDING TYPE 14--REINFORCED MASONRY WALLS
WITH PRECAST CONCRETE DECK Floor Roof Vertical-Resisting Diaphragm Elements Foundations Connections Precast concrete units Reinforced masonry Spread footings, piles, Diagonal wire or strut bracing
(planks, cored slabs, walls. or drilled piers. bracing of ceilings from floor tees, etc.) roof diaphragms.
Bracing or lateral support of 
walls and partitions from ceilings or diaphragms.
Connection of precast floor roof units to shear walls.
Connections between adjacent precast floor roof units.
Tension ties or hold-downs for masonry walls.
163 
TABLE A15 STRUCTURAL ELEMENTS OF COMMON BUILDING TYPE 15-UNREINFORCED MASONRY BEARING WALLS Floor Roof Vertical-Resisting Diaphragm Elements Foundations Connections 
Timber framing with Unreinforced masonry Spread footings, piles, Diagonal wire or strut plywood, straight-laid, walls. or drilled piers. bracing of ceilings from floor or diagonal sheathing. roof diaphragms.
Reinforced concrete Bracing or lateral support of slab supported on walls and partitions from structural steel floor ceilings or diaphragms.
framing members.
Connection of timber or Reinforced concrete floor roof slab monolithic with diaphragms to masonry walls.
reinforced concrete beams and girders. Development of diaphragm chords in timber or concrete floor roof diaphragms.
Tension ties or hold-downs for masonry walls.
164 

APPENDIX B
SUMMARY OF STRENGTHENING TECHNIQUES
The deficiencies and alternative strengthening techniques discussed in Chapter 3 are summarized here as follows: 
Table Bi Moment Resisting Systems 
Steel Moment Frames 
Concrete Moment Frames 
Moment Frames with Infill Walls 
Precast Concrete Moment Frames 
Table B2 Shear Walls 
Reinforced Concrete or Reinforced Masonry 
Precast Concrete 
Unreinforced Masonry 
Shear Walls in Wood Frame Buildings 
Table B3 Braced Frames 
Table B4 Diaphragms 
Table B5 Foundations 
Table B6 Diaphragm to Vertical Element Connections 
Table B7 Vertical Element to Foundation Connections 
165 
TABLE Bi 
MOMENT RESISTING SYSTEMS 
STEEL MOMENT FRAMES 
Deficiency 
Inadequate moment/shear capacity 
of beams, columns, or their connections 
Inadequate beam/column panel zone 
capacity 
Excessive drift 
Strengthening Techniques 
1. Increasing the moment capacity of the members and connections 
by adding cover plates or other steel sections to the 
flanges Or by boxing members. 
2. Increasing the moment and shear capacity of the members 
and connections by providing steel gusset plates or knee 
braces. 
3. Reducing the stresses in the existing frames by providing 
supplemental vertical-resisting elements (i.e., additional moment 
frames, braces, or shear walls) as discussed in Sec. 3.4. 
4. Providing lateral bracing of unsupported flanges to increase 
capacity limited by tendency for lateral/torsional buckling. 
5. Encasing the columns in concrete. 
1. Providing welded continuity plates between the column flanges. 
2. Providing stiffener plates welded to the column flanges and 
web. 
3. Providing web doubler plates at the column web. 
4. Reducing the stresses in the panel zone by providing supplemental 
vertical-resisting elements (i.e., additional moment 
frames, braces, or shear walls) as discussed in Sec. 3.4. 
1. Increasing the capacity and, hence, the stiffness of the existing 
moment frame by cover plates or boxing. 
2. Increasing the stiffness of the beams and columns at their 
connections by providing steel gusset plates to form haunches. 
3. Reducing the drift by providing supplemental vertical-resisting elements (i.e., additional moment frames, braces, or 
shear walls) as discussed in Sec. 3.4. 
4. Increasing the stiffness by encasing columns in reinforced 
concrete. 
5. Reducing the drift by adding supplemental damping as discussed 
in Sec. 4. 
CONCRETE MOMENT FRAMES
Inadequate ductile bending or shear 
capacity in the beams or columns 
and lack of confinement, frequently 
in the joints 
1. Increasing the ductility and capacity by jacketing the beam 
and column joints or increasing the beam or column capacities. 
2. Reducing the seismic stresses in the existing frames by providing 
supplemental vertical-resisting elements (i.e., additional 
moment frames, braces, or shear walls) as discussed in 
Sec. 3.4. 
3. Changing the system to a shear wall system by infilling the 
reinforced concrete frames with reinforced concrete. 
166 
TABLE Bl--continued 
MOMENT FRAMES WITH INFILL WALLS 
Crushing of the infill at the upper 1. Eliminating the hazardous effects of the infill by providing a 
and lower corners due to the gap between the infill and the frame and providing out-of- diagonal compression strut type action plane support. 
of the infill wall 2. * Treating the frame as a shear wall and correcting the 
deficiencies as described in Sec. 3.2.
Shear failure of the beam/column 
connection in the steel frames or 
direct shear transfer failure of the 
beam or column in concrete frames 
Tensile failure of the columns or 
their connections due to the uplift 
forces resulting from the braced 
frame action induced by the infill 
Splitting of the infill due to the orthogonal 
tensile stresses developed in 
the diagonal compressive strut 
Loss of infill by out-of-plane forces 
due to loss of anchorage or excessive 
slenderness of the infill wall 
PRECAST CONCRETE MOMENT FRAMES 
Inadequate capacity and/or ductility 
1. Removing existing concrete in the precast elements to expose 
of the joints between the precast the existing reinforcing steel, providing additional reinforcing 
units steel welded to the existing steel (or drilled and grouted), 
and replacing the removed concrete with cast-in-place concrete. 
2. Reducing the forces on the connections by providing supplemental 
vertical-resisting elements (i.e., additional moment 
frames, braces, or shear walls) as discussed in Sec. 3.4. 
167 
REINFORCED 
Deficiency 
Inadequate shear capacity 
Inadequate flexural capacity 
TABLE B2 
SHEAR WALLS 
CONCRETE OR REINFORCED MASONRY SHEAR WALLS 
Strengthening Techniques 
1. Increasing the effectiveness of the existing walls by filling in 
door or window openings with reinforced concrete or masonry. 
2. Providing additional thickness to the existing walls with a 
poured-in-place or pneumatically applied (i.e., shotcrete) 
reinforced concrete overlay anchored to the inside or outside 
face of the existing walls. 
3. Reducing the shear or flexural stresses in the existing walls 
by providing supplemental vertical-resisting elements (i.e., 
shear walls, braces, or external buttresses) as discussed in 
Sec. 3.4. 
1. Increasing the effectiveness of the existing walls by filling in 
door or window openings with reinforced concrete or masonry. 
2. Providing additional thickness to the existing walls with a 
poured-in-place or pneumatically applied (i.e., shotcrete) 
reinforced concrete overlay anchored to the inside or outside 
face of the existing walls. 
3. Reducing the shear or flexural stresses in the existing walls 
by providing supplemental vertical-resisting elements (i.e., 
shear walls, braces, or external buttresses). as discussed in 
Sec. 3.4. 
Inadequate shear or flexural capacity 1. Eliminating the coupling beams by filling in openings with 
in the coupling beams between shear reinforced concrete. 
walls or piers 
Inadequate shear 
in the wall panels 
2. Removing the existing beams and replacing with new stronger 
reinforced beams. 
3. Adding reinforced concrete to one or both faces of the wall 
and providing an additional thickness to the existing wall. 
4. Reducing the shear or flexural stresses in the connecting 
beams by providing additional vertical-resisting elements (i.e., 
shear walls, braces, or external buttresses) as discussed in 
Sec. 3.4. 
PRECAST CONCRETE SHEAR WALLS 
or flexural capacity 
1. Increasing the shear and flexural capacity of walls with significant 
openings for doors or windows by infilling the existing 
openings with reinforced concrete. 
2. Increasing the shear or flexural capacity by adding reinforced 
concrete (poured-in-place or shotcrete) at the inside or outside 
face of the existing walls. 
3. Adding interior shear walls to reduce the flexural or shear 
stress in the existing precast panels. 
168 
TABLE B2--continued 
PRECAST CONCRETE SHEAR WALLS-continued 
Inadequate interpanel shear or flex-1. Making each panel act as a cantilever to resist in-plane capacity forces (by adding or strengthening tie-downs, edge reinforcement, footings). 
2. Providing a continuous wall by exposing the reinforcing steel 
in the edges of adjacent units, adding ties, and repairing with 
concrete. 
Inadequate out-of-plane flexural 
1. Providing pilasters at and/or between the interpanel joints. 
capacity 
2. Adding horizontal beams between the columns or pilasters at 
mid-height of the wall. 
Inadequate shear or flexural capacity 
1. Eliminating the coupling beams by filling in openings with 
in coupling beams reinforced concrete. 
2. Removing the existing beams and replacing with new stronger 
reinforced beams. 
3. Adding reinforced concrete to one or both faces of the wall 
and providing an additional thickness to the existing wall. 
4. Reducing the shear or flexural stresses in the connecting 
beams by providing additional vertical-resisting elements (i.e., 
shear walls, braces, or external buttresses) as discussed in 
Sec. 3.4.2 
UNREINFORCED MASONRY SHEAR WALLS 
Inadequate in-plane shear and out-
1. Providing additional shear capacity by placing reinforcing 
of-plane flexural capacity of the walls steel on the inside or outside face of the wall and applying 
new reinforced concrete. 
2. Providing additional capacity for out-of-plane lateral forces 
by adding reinforcing steel to the wall utilizing the center 
coring technique. 
3. Providing additional capacity for out-of-plane lateral forces 
by adding thin surface treatments (e.g., plaster with wire 
mesh and portland cement mortar) at the inside and outside 
faces of existing walls. 
4. Filling in existing window or door openings with reinforced 
concrete. 
5. Providing additional shear walls at the interior or perimeter 
of the building or providing external buttresses. 
Inadequate shear capacity of the 
1. Filling in openings with reinforced concrete. 
coupling beam 
2. Removing existing connecting beams and replacing them 
with properly designed new reinforced concrete beams. 
3. Providing additional shear walls at interior or perimeter of 
building or external buttresses. 
169 
TABLE B2--continued 
SHEAR WALIS IN WOOD FRAME BUILDINGS 
Inadequate shear capacity of the wall 
1. Increasing the shear capacity by providing additional nailing 
to the existing finish material. 
2. Increasing the shear capacity by adding plywood sheathing to 
* one or both sides of the wall. 
3. Reducing the loads on the wall by providing supplemental 
shear walls to the interior or perimeter of the building. 
Inadequate uplift or hold-down ca-1. Increasing the tensile capacity of the connections at the edge 
of the shear walls by providing metal connectors.
pacity of the wall 
2. Reducing the overturning moments by providing supplemental 
vertical-resisting elements as discussed in Sec. 3.4. 
'W 
170 
TABLE B3 
BRACED FRAMES 
STEEL CONCENTRICALLY BRACED FRAMES 
(including chevron or K-bracing) 
Deficiency Strengthening Techniques 
Inadequate lateral force capacity of 
1. Increasing the capacity of the braces by adding new members 
the bracing system governed by buck- thus increasing the area and reducing the radius of gyration 
ling of the compression brace of the braces. 
2. Increasing the capacity of the member by reducing the unbraced 
length of the existing member by providing secondary 
braces. 
3. Providing greater capacity by removing and replacing the 
existing members with new members of greater capacity. 
4. Reducing the loads on the braces by providing supplemental 
vertical-resisting elements (i.e., shear walls, braces, or eccentric 
bracing) as discussed in Sec. 3.4. 
Inadequate capacity of the brace 
1. Increasing the capacity of the connections by additional bolt-
connection ing or welding. 
2. Increasing the capacity of the connections by removing and 
replacing the connection with members of greater capacity. 
3. Reducing the loads on the braces and their connections by 
providing supplemental vertical-resisting elements (i.e., shear 
walls, braces, or eccentric bracing) as discussed in Sec. 3.4. 
Inadequate axial load capacity in the 
1. Providing additional axial load capacity by adding cover 
columns or beams of the bracing plates to the member flanges or by boxing the flanges. 
system 
2. Providing additional axial load capacity by jacketing the existing 
members with reinforced concrete. 
3. Reducing the loads on the beams and columns by providing 
supplemental vertical-resisting elements (i.e., shear walls, 
braces, or eccentric bracing) as discussed in Sec. 3.4. 
171 
TABLE B3-continued 
ROD OR OTHER TENSION BRACING 
Inadequate tension capacity of the 
1. Increasing the capacity by strengthening the existing tension 
rod, tensile member, or its members. 
connection 
2. Increasing the capacity by removing the existing tension 
members and replacing with new members of greater capacity. 
3. Increasing the capacity by removing the existing tension 
member and replacing it with diagonal or X-bracing capable 
of resisting compression as well as tension forces. 
4. Reducing the forces on the existing tension members by 
providing supplemental vertical-resisting elements (i.e., additional 
tension rods) as discussed in Sec. 3.4. 
Inadequate axial capacity of the 
1. Increasing the axial capacity by adding cover plates to the 
beams or columns in the bracing existing flanges or by boxing the existing flanges. 
system 
2. Reducing the forces on the existing columns or beams by 
providing supplemental vertical-resisting elements (i.e., 
braced frames or shear walls) as discussed in Sec. 3.4. 
ECCENTRIC BRACING 
Nonconformance with current design 
1. Ensuring that the system is balanced (i.e., there is a link 
standards beam at one end of each brace), the brace and the connections 
are designed to develop shear or flexural yielding in the 
link, the connection is a full moment connection, where the 
link beam has an end at a column, and lateral bracing is 
provided to prevent out-of-plane beam displacements that 
would compromise the intended action. 
2. Providing supplemental vertical-resisting elements such as 
additional eccentric braced frames. 
172 
Deficiency 
Inadequate shear capacity of the 
diaphragm 
Inadequate chord capacity of the 
diaphragm 
Excessive shear stresses at diaphragm openings or at plan irregularities 
Inadequate stiffness of the diaphragm resulting in excessive diaphragm 
deformations 
Inadequate 
the concrete diaphragm 
TABLE B4 
DIAPHRAGMS 
TIMBER DIAPHRAGMS 
(straight-laid or diagonal sheathing or plywood) 
Strengthening Techniques 
1. Increasing the capacity of the existing timber diaphragm by 
providing additional nails or staples with due regard for 
wood splitting problems. 
2. Increasing the capacity of the existing timber diaphragm by 
means of a new plywood overlay. 
3. Reducing the diaphragm span through the addition of supplemental 
vertical-resisting elements (i.e., shear wall or 
braced frames) as discussed in Sec. 3.4. 
1. Providing adequate nailed or bolted continuity splices along 
joists or fascia parallel to the chord. 
2. Providing a new continuous steel chord member along the 
top of the diaphragm. 
3. Reducing the stresses on the existing chords by reducing the 
diaphragms, span through the addition of new shear walls or 
braced frames as discussed in Sec. 3.4. 
1. Reducing the local stresses by distributing the forces along 
the diaphragm by means of drag struts. 
2. Increasing the capacity of the diaphragm by overlaying the 
existing diaphragm with plywood and nailing the plywood 
through the sheathing at the perimeter of the sheets adjacent 
to the opening or irregularity. 
3. Reducing the diaphragm stresses by reducing the diaphragm 
spans through the addition of supplemental shear walls or 
braced frames as discussed in Sec. 3.4. 
1. Increasing the stiffness of the diaphragm by the addition of a 
new plywood overlay. 
2. Reducing the diaphragm span and hence reducing the displacements 
by providing new supplemental vertical-resisting 
elements such as shear walls or braced frames as discussed 
in Sec. 3.4. 
CONCRETE DIAPHRAGMS 
(monolithic concrete diaphragms--i.e., reinforced concrete or post-tensioned concrete) 
in-plane shear capacity of 
1. Increasing the shear capacity by overlaying the existing concrete 
diaphragm with a new reinforced concrete topping slab. 
2. Reducing the shear in the existing concrete diaphragm by 
providing supplemental vertical-resisting elements (i.e., shear 
walls or braced frames) as discussed in Sec. 3.4. 
173 
TABLE B4--continued 
Inadequate diaphragm chord capacity 
Excessive shear stresses at the diaphragm openings or plan irregularities 
1. Increasing the flexural capacity by removing the edge of the 
diaphragm slab and casting a new chord member integral 
with the slab. 
2. Adding a new chord member by providing a new reinforced 
concrete or steel member above or below the slab and connecting 
the new member to the existing slab with drilled and 
grouted dowels or bolts as discussed in Sec. 3.5.4.3. 
3. Reducing the existing flexural stresses by providing supplemental 
vertical-resisting elements (i.e., shear walls or braced 
frames) as discussed in Sec. 3.4. 
1. Reducing the local stresses by distributing the forces along 
the diaphragm by means of structural steel or reinforced 
concrete elements cast beneath the slab and made integral 
through the use of drilled and grouted dowels. 
2. Increasing the capacity of the concrete by providing a new 
concrete topping slab in the vicinity of the opening and reinforcing 
with trim bars. 
3. Removing the stress concentration by filling in the diaphragm 
opening with reinforced concrete. 
4. Reducing the shear stresses at the location of the openings 
by adding supplemental vertical-resisting elements (i.e., shear 
walls or braced frames) as discussed in Sec. 3.4. 
174 
TABLE B4--continued 
POURED GYPSUM DIAPHRAGMS 
Inadequate in-plane shear capacity of 
the concrete diaphragm 
Inadequate diaphragm chord capacity 
Excessive shear stresses at the diaphragm 
openings or plan irregularities 
1. Increasing the shear capacity by overlaying the existing concrete 
diaphragm with a new reinforced concrete topping slab. 
2. Reducing the shear in the existing concrete diaphragm by 
providing supplemental vertical-resisting elements (i.e., shear 
walls or braced frames) as discussed in Sec. 3.4. 
3. Increasing the flexural capacity by removing the edge of the 
diaphragm slab and casting a new chord member integral 
with the slab. 
4. Adding a new chord member by providing a new reinforced 
concrete or steel member above or below the slab and connecting 
the new member to the existing slab with drilled and 
grouted dowels or bolts as discussed in Sec. 3.5.4.3. 
5. Reducing the existing flexural stresses by providing supplemental 
vertical-resisting elements (i.e., shear walls or braced 
frames) as discussed in Sec. 3.4. 
6. Reducing the local stresses by distributing the forces along 
the diaphragm by means of structural steel or reinforced 
concrete elements cast beneath the slab and made integral 
through the use of drilled and grouted dowels. 
7. Increasing the capacity of the concrete by providing a new 
concrete topping slab in the vicinity of the opening and reinforcing 
with trim bars. 
8. Removing the stress concentration by filling in the diaphragm 
opening with reinforced concrete. 
9. Reducing the shear stresses at the location of the openings 
by adding supplemental vertical-resisting elements (i.e., shear 
walls or braced frames) as discussed in Sec. 3.4. 
10. Adding a new horizontal bracing system may be the most 
effective strengthening alternative. 
PRECAST CONCRETE DIAPHRAGMS 
(precast or post-tensioned concrete planks, tees, or cored slabs) 
Inadequate in-plane shear capacity of 
the connections between the adjacent 
units 
1. 
2. 
Replacing and increasing the capacity of the existing connections 
by overlaying the existing diaphragm with a new reinforced 
concrete topping slab. 
Reducing the shear forces on the diaphragm by providing 
supplemental vertical-resisting elements (i.e., shear walls or 
braced frames) as discussed in Sec. 3.4. 
Inadequate diaphragm chord capacity 1. Providing a new continuous steel member above or below 
the steel slab and connecting the new member to the existing 
slab with bolts. 
2. 
3. 
Removing the edge of the diaphragm and casting a new 
chord member integral with the slab. 
Reducing the diaphragm chord forces by providing supplemental 
vertical-resisting elements (i.e., shear walls or braced 
frames) as discussed in Sec. 3.4. 
175 
diaphragm openings or plan irregularities 
Inadequate in-plane shear capacity 
TABLE B4--continued 
PRECAST CONCRETE DLAPHRAGMS--continued 
Excessive in-plane shear stresses at 1. Reducing the local stresses by distributing the forces along 
the diaphragm by means of concrete drag struts cast beneath 
the slab and made integral with the existing slab with drilled 
and grouted dowels. 
2. Increasing the capacity by overlaying the existing slab with a 
new reinforced concrete topping slab with reinforcing trim 
bars in the vicinity of the opening. 
3. Removing the stress concentration by filling in the diaphragm 
opening with reinforced concrete. 
4. Reducing the shear stresses at the location of the openings 
by providing supplemental vertical-resisting elements (i.e., 
shear walls or braced frames) as discussed in Sec. 3.4. 
& 
STEEL DECK DIAPHRAGMS 
(steel decking on steel framing) 
which may be governed by the capacity of the welding to the supports or 
the capacity of the seam welds between the deck units 
Inadequate diaphragm chord capacity 
Excessive in-plane shear stresses at 
diaphragm openings or plan irregularities 
1. Increasing the steel deck shear capacity by providing additional 
welding. 
2. Increasing the deck shear capacity of unfilled steel decks by 
adding a reinforced concrete fill or overlaying with concrete 
filled steel decks a new topping slab. 
3. Increasing the diaphragm shear capacity by providing a new 
horizontal steel bracing system under the existing diaphragm. 
4. Reducing the diaphragm shear stresses by providing supplemental 
vertical-resisting elements to reduce the diaphragm 
span as discussed in Sec. 3.4. 
1. Increasing the chord capacity by providing welded or bolted 
continuity splices in the perimeter chord steel framing members. 
2. Increasing the chord capacity by providing a new continuous 
steel member on top or bottom of the diaphragm. 
3. Reducing the diaphragm chord stresses by providing supplemental 
vertical-resisting elements (i.e., shear walls or braced 
frames) such that the diaphragm span is reduced as discussed 
in Sec. 3.4. 
1. Reducing the local stress concentrations by distributing the 
forces into the diaphragm by means of steel drag struts. 
2. Increasing the capacity of the diaphragm by reinforcing the 
edge of the opening with a steel angle frame welded to the 
decking. 
3. Reducing the diaphragm stresses by providing supplemental 
vertical-resisting elements (i.e., shear walls, braced frames or 
new moment frames) such that the diaphragm span is reduced 
as discussed in Sec. 3.4. 
176 
TABLE B4-continued 
HORIZONTAL STEEL BRACING 
*1 Inadequate force capacity of the 
1. Increasing the capacity of the existing bracing members or 
members (i.e., bracing and floor or removing and replacing them with new members and roof beams) and/or the connections connections of greater capacity. 
2. Increasing the capacity of the existing members by reducing 
unbraced lengths. 
3. Increasing the capacity of the bracing system by adding new 
horizontal bracing members to previously unbraced panels (if 
feasible). 
4. Increasing the capacity of the bracing system by adding a 
steel deck diaphragm to the floor system above the steel 
bracing. 
5. Reducing the stresses in the horizontal bracing system by 
providing supplemental vertical-resisting elements (i.e., shear 
walls or braced frames) as discussed in Sec. 3.4. 
177 
TABLE BS 
FOUNDATIONS 
CONTINUOUS OR STRIP WALL FOOTINGS 
Deficiency 
Excessive soil bearing pressure due 
to overturning forces 
Excessive uplift conditions due to 
overturning forces 
Strengthening Techniques 
1. Increasing the bearing capacity of the footing by underpinning 
the footing ends and providing additional footing area. 
2. Increasing the vertical capacity of the footing by adding new 
drilled piers adjacent and connected to the existing footing. 
3. Increasing the soil bearing capacity by modifying the existing 
soil properties. 
4. Reducing the overturning forces by providing supplemental 
vertical-resisting elements (i.e., shear walls or braced frames) 
as discussed in Sec. 3.4. 
1. Increasing the uplift capacity of the existing footing by adding 
drilled piers or soil anchors. 
2. Increasing the size of the existing footing by underpinning to 
mobilize additional foundation and reduce soil pressures. 
3. Reducing the uplift forces by providing supplemental vertical-resisting elements (i.e., shear walls or braced frames) as 
discussed in Sec. 3.4. 
INDIVIDUAL PIER OR COLUMN FOOTINGS
Excessive soil bearing pressure due 
to overturning forces 
Excessive uplift conditions due to 
overturning forces 
1. Increasing the bearing capacity of the footing by underpinning 
the footing ends and providing additional footing area. 
2. Increasing the vertical capacity of the footing by adding new 
drilled piers adjacent and connected to the existing footing. 
3. Reducing the bearing pressure on the existing footings by 
connecting adjacent footings with deep reinforced concrete 
tie beams. 
4. Increasing the soil bearing capacity by modifying the existing 
soil properties. 
5. Reducing the overturning forces by providing supplemental 
vertical-resisting elements (i.e., shear walls or braced 
frames). 
1. Increasing the uplift capacity of the existing footing by adding 
drilled piers or soil anchors. 
2. Increasing the size of the existing footing by underpinning to 
mobilize additional foundation and soil weight. 
3. Increasing the uplift capacity by providing a new deep reinforced 
concrete beam to mobilize the dead load on an adjacent 
footing. 
4. Reducing the uplift forces by providing supplemental vertical-resisting elements (i.e., shear walls or braced frames). 
178 
TABLE BS--continued 
INDIVIDUAL PIER OR COLUMN FOOTINGS--continued 
Inadequate passive soil pressure to 1. Providing an increase in bearing area by underpinning and 
resist lateral loads 
Excessive tensile or compressive 
loads on the piles or piers due to the 
seismic forces combined with the 
gravity loads 
Inadequate lateral force capacity to 
transfer the seismic shears from the 
pile caps and the piles to the soil 
Inadequate moment capacity to resist 
combined gravity plus seismic over-
turning forces 
Inadequate passive soil pressure to 
resist sliding 
enlarging the footing. 
2. Providing an increase in bearing area by adding new tie 
beams between existing footings. 
3. Improving the existing soil conditions adjacent to the footing 
to increase the allowable passive pressure. 
4. Reducing the bearing pressure at overstressed locations by 
providing supplemental vertical-resisting elements such as 
shear walls or braced frames as discussed in Sec. 3.4. 
PILES OR DRILLED PIERS 
1. Increasing the capacity of the foundation by removing the 
existing pile cap, driving additional piles and providing new 
pile caps of larger size. 
2. Reducing the loads on overstressed pile caps by adding tie 
beams to adjacent pile caps and distributing the loads. 
1. Reducing the loads on overstressed pile caps by adding tie 
beams to adjacent pile caps and distributing the loads. 
2. Increasing the allowable passive pressure of the soil by improving 
the soil adjacent to the pile cap. 
3. Increasing the capacity of the foundation by removing the 
existing pile cap, driving additional piles, and providing new 
pile caps of larger size. 
4. Reducing loads on the piles or piers by providing supplemental 
vertical-resisting elements (i.e., braced frames or shear 
walls) and transferring forces to other foundation members 
with reserve capacity as discussed in Sec. 3.4. 
MAT 
1. Increasing the mat capacity locally by providing additional 
reinforced concrete (i.e., an inverted column capital) doweled 
and bonded to the existing mat to act as a monolithic section. 
2. Providing new shear walls above the mat to distribute the 
overturning loads and also to locally increase the section 
modulus of the mat. 
1. Constructing properly spaced shear keys at the mat perimeter. 
179 
TABLE B6 
DIAPHRAGM TO VERTICAL ELEMENT CONNECTIONS 
CONNECTIONS OF TIMBER DIAPHRAGMS 
Deficiency 
Inadequate capacity to transfer 
in-plane shear at the connection of 
the diaphragm to interior shear walls 
or vertical bracing 
Inadequate capacity to transfer 
in-plane shear at the connection of 
the diaphragm to exterior shear walls 
or vertical bracing 
Inadequate out-of-plane anchorage at 
the connection of the diaphragm to 
exterior concrete or masonry walls 
Inadequate tensile capacity between 
floors due to overturning moments 
Strengthening Techniques 
1. Increasing the shear transfer capacity of the diaphragm local 
to the connection by providing additional nailing to existing 
or new blocking. 
2. Reducing the local shear transfer stresses by distributing the 
forces from the diaphragm by providing a collector member 
to transfer the diaphragm forces to the shear wall. 
3. Reducing the shear transfer stress in the existing connection 
by providing supplemental vertical-resisting elements as discussed 
in Sec. 3.4. 
1. Increasing the capacity of existing connections by providing 
additional nailing and/or bolting. 
2. Reducing the local shear transfer stresses by distributing the 
forces from the diaphragm by providing chords or collector 
members to collect and distribute shear from the diaphragm 
to the shear wall or bracing. 
3. Reducing the shear stress in the existing connection by providing 
supplemental vertical-resisting elements as discussed 
in Sec. 3.4. 
1. Increasing the capacity of the connection by providing steel 
straps connected to the wall (using drilled and grouted bolts 
or through bolts for masonry walls) and bolted or lagged to 
the diaphragm or roof or floor joists. 
2. Increasing the capacity of the connections by providing a 
steel anchor to connect the roof or floor joists to the walls. 
3. Increasing the redundancy of the connection by providing 
continuity ties into the diaphragm. 
1. Increasing the tensile capacity of the connections at the edge 
of the shear walls by providing metal connectors. 
2. Reducing the overturning moments by providing supplemental 
vertical-resisting elements as discussed in Sec. 3A. 
180 
TABLE B6--continued 
CONNECTIONS OF CONCRETE DIAPHRAGMS 
Inadequate in-plane shear transfer 1. Reducing the local stresses at the diaphragm-to-wall inter-
capacity face by providing collector members or drag struts under the 
diaphragm and connecting them to the diaphragm and the 
wall. 
2. Increasing the capacity of the existing diaphragm-to-wall 
connection by providing additional dowels grouted into 
drilled holes. 
3. Reducing the shear stresses in the existing connection by 
providing supplemental vertical-resisting elements as discussed 
in Sec. 3.4. 
Inadequate anchorage capacity for 
1. Increasing the capacity of the connection by providing out-of-plane forces in the connecting additional dowels grouted into drilled holes. walls 
2. Increasing the capacity of the connection by providing a new 
member above or below the slab connected to the slab with 
drilled and grouted bolts similar to that for providing a new 
diaphragm chord. 
CONNECTIONS OF POURED GYPSUM DIAPHRAGMS 
Inadequate in-plane shear transfer 1. Providing new dowels from the diaphragm into the shear 
wall. 
2. Removing the gypsum diaphragm and replacing it with steel 
decking. 
Inadequate anchorage capacity for 
3. Adding a new horizontal bracing system designed to resist all 
out-of-plane forces in the connecting of the seismic forces. 
walls 
CONNECTIONS OF PRECAST CONCRETE DIAPHRAGMS 
Inadequate in-plane shear transfer 1. Increasing the capacity of the connection by providing capacity additional welded inserts or dowels placed in drilled or grouted holes. 
2. Increasing the capacity of the connection by providing a 
reinforced concrete overlay that is bonded to the precast 
Inadequate anchorage capacity at the units and anchored to the wall with additional dowels placed 
exterior walls for out-of-plane forces in drilled and grouted holes. 
3. Reducing the forces at the connection by providing supplemental 
vertical-resisting elements as discussed in Sec. 3.4. 
181 
TABLE B6--continued 
CONNECTIONS OF STEEL DECK DIAPHRAGMS WITHOUT CONCRETE FILL 
Inadequate in-plane shear capacity or 1. Increasing the capacity of the connection by providing anchorage 
capacity for out-of-plane additional welding at the vertical element. 
forces in walls 2. Increasing the capacity of the connection by providing additional 
anchor bolts. 
3. Increasing the capacity of the connection by providing concrete 
fill over the deck with dowels grouted into holes drilled 
into the wall. 
4. Increasing the capacity of the connection by providing new 
steel members to effect a direct transfer of diaphragm shears 
to a shear wall. 
5. Reducing the local stresses by providing additional vertical-
resisting elements such as shear walls, braced frames, or 
moment frames as discussed in Sec. 3.4. 
CONNECTIONS OF STEEL DECK DIAPHRAGMS WITH CONCRETE FILL 
Inadequate in-plane shear capacity or 1. Increasing the shear capacity by drilling holes through the 
anchorage capacity for out-of-plane concrete fill, and providing additional shear studs welded to 
forces in walls the vertical elements through the decking. 
2. Increasing the capacity of the connection by providing additional 
anchor bolts (drilled and grouted) connecting the steel 
support to the wall. 
3. Increasing the capacity of the connection by placing dowels 
between the existing wall and diaphragm slab. 
4. Reducing the local stresses by providing additional vertical-
resisting elements such as shear walls, braced frames, or 
moment frames as discussed in Sec. 3.4. 
CONNECTIONS OF HORIZONTAL STEEL BRACING 
Inadequate in-plane shear transfer 
1. Increasing the capacity by providing larger or more bolts or 
capacity by welding. 
2. Reducing the stresses by providing supplemental vertical-
resisting elements such as shear walls or braced frames as 
discussed in Sec. 3.4. 
Inadequate anchorage capacity when 
1. Increasing the capacity of the connection by providing supporting 
concrete or masonry walls additional anchor bolts grouted in drilled holes and by providing 
for out-of-plane forces more bolts or welding to the bracing members. 
182 
TABLE B7 
VERTICAL ELEMENT TO FOUNDATION CONNECTIONS 
CONNECTIONS OF WOOD STUD SHEAR WALLS 
Inadequate 
anchorage 
Inadequate 
stud walls 
Inadequate 
Inadequate 
anchorage 
Inadequate 
stud walls 
Inadequate 
Inadequate 
Deficiency 
shear capacity of the 
shear capacity of cripple 
uplift capacity 
Strengthening Techniques 
1. Increasing the shear capacity by providing new or additional 
anchor bolts between the sill plate and the foundation. 
2. Increasing the shear capacity by providing steel angles or 
plates with anchor bolts connecting them to the foundation 
and bolts or lag screws connecting them to the sill plate or 
wall. 
1. Adding plywood sheathing over the cripple studs (usually on 
the inside) by nailing into the floor framing and the sill plate. 
Anchorage of the sill plate to the foundation also must be 
provided. 
1. Increasing the capacity by providing steel hold-downs bolted 
to the wall and anchored to the concrete. 
2. Reducing the uplift requirement by providing supplemental 
shear walls as discussed in Sec. 3.4. 
CONNECTIONS OF METAL STUD SHEAR WALLS 
shear capacity of the 
shear capacity of cripple 
uplift capacity 
1. Provide anchor bolts, grouted in drilled holes, through sill 
plate of wall. 
2. Provide steel angles with anchor bolts to concrete and bolts 
or screws to wall. 
1. Provide plywood sheathing, nailing into cripple studs, sill 
plate, and first floor framing; anchor sill plate to foundation. 
1. Provide steel hold-down with bolts or screws to wall and 
anchor bolts to concrete at ends of shear wall. 
2. Provide additional shear walls or vertical bracing. 
CONNECTIONS OF PRECAST CONCRETE SHEAR WALLS 
capacity to resist in-plane 1. Increasing the capacity of the connection by providing a new 
or out-of-plane shear forces steel member connecting the wall to the foundation or the 
ground floor slab. 
2. Increasing the capacity of the connection by adding a new 
thickness of concrete (either cast-in-place or shotcrete) 
placed against the precast wall doweling into the existing 
foundation or ground floor slab. 
183 
TABLE B7-continued 
CONNECTIONS OF PRECAST CONCRETE SHEAR WALLS--continued 
Inadequate hold-down capacity to 
1. Increase the hold-down capacity by removing concrete at the 
resist seismic overturning forces edge of the precast unit to expose the reinforcement provide, 
new drilled and grouted dowels into the foundation, and 
pour a new concrete pilaster. 
2. Reduce the uplift forces by providing supplemental vertical-
resisting elements such as shear walls or braced frames as 
discussed in Sec. 3.4. 
CONNECTIONS OF BRACED FRAMES 
Inadequate shear capacity 
1. Increasing the capacity by providing new steel members 
welded to the braced frame base plates and anchored to the 
slab or foundation with drilled and grouted anchor bolts. 
2. Reducing the shear loads by providing supplemental steel 
braced frames as discussed in Sec. 3.4. 
Inadequate uplift resistance 
1. Increasing the capacity by providing new steel members 
welded to the base plate and anchored to the existing foundation. 
2. Reducing the uplift loads by providing supplemental steel 
braced frames as discussed in Sec. 3.4. 
CONNECTIONS OF STEEL MOMENT FRAMES 
Inadequate shear capacity 
1. Increasing the shear capacity by providing steel shear lugs 
welded to the base plate and embedded in the foundation. 
2. Increasing the shear and tensile capacity by installing 
Inadequate flexural capacity additional anchor bolts into the foundation. 
3. Increasing the shear capacity by embedding the column in a 
Inadequate uplift capacity reinforced concrete pedestal that is bonded or embedded 
into the existing slab or foundation. 
184 

APPENDIX C
REHABILITATION EXAMPLES
Two examples are included in this appendix to demonstrate the process of selecting appropriate seismic rehabilitation techniques: a two-story steel frame building and a two story unreinforced masonry building. Both buildings were evaluated to determine their seismic deficiencies in accordance with the NEHRP Handbook for the Seismic Evaluation of Existing Buildings (which includes the evaluations as Examples D1 and D6 in Appendix D). STORY STEEL FRAME BUILDING EXAMPLE C1.1 DESCRIPTION OF BUILDING The building is 200 ft by 340 ft in plan with 20 ft by 20 ft bays. The girders in the transverse direction are connected to the column flanges with top and bottom clip angles. The beams in the longitudinal direction are connected to the column webs with beam web connections. The floor and roof diaphragms consists of steel decking with concrete fill.
C12 DEFICIENCIES Inadequate moment capacity in both directions.
C13 STRENGTHENING ALTERNATIVES This building could be strengthened by providing adequate moment capacity to the existing frames, by providing new diagonal bracing, and/or by providing new shear walls C13.1 Providing Adequate Moment Capacity Assuming that the first story shear of 2,970 kips can be equally distributed to all columns, it is calculated that there is excess capacity for the columns in the transverse direction (i.e., the strong axis of the columns) but grossly inadequate capacity for the columns in the longitudinal direction (i.e., the weak axis of the columns).
This indicates that it is not feasible to develop adequate frame action to resist the seismic forces in the longitudinal direction, but it is feasible in the transverse direction. The structural modifications (Figure C1.3.1) required to develop moment frame action will involve: 
1. Removal of the concrete fill and steel decking over the ends of the transverse girders at the columns. (It is assumed that the steel decking is supported on secondary floor beams that frame into the transverse frame girders so that there are no adverse effects associated with removal of the decking over top flanges of these girders adjacent to the columns.) The American Iron and Steel Institute has written a minority opinion concerning this appendix; see page 193.
185 
2. Addition of new vertical shear connections between the girder webs and the column flanges.
3. Removal of existing clip angles at the top and bottom flanges of the girders.
4. Addition of new moment plates welded at the top and bottom flanges of the girders.
(E) transverse =girder (N) web shear connection (E) clip angles, to be removed. removed (E) longitudinal beam SECTION a-a (E) transverse girder (N) moment plate (E) longitudinal Remove (E) concrete beam fill and steel decking PLAN FIGURE C1.3.1 Providing moment capacity to an existing steel frame.
The design of these modifications should provide moment plates that are sized so as to yield prior to inducing yield stress in the columns. The new girder web shear connections should be sized for the gravity load shears (i.e., dead and live load) plus the shears associated with the formation of yield hinges in the moment plates. The column section of the new frame joint must be checked to determine the possible need for horizontal stiffeners opposite the girder flanges. The column web also should be checked to determine the need for doubler plates. Stiffeners probably can be fitted above or below the existing longitudinal beam-, at the column, but if doubler plates are required, this alternative may not be feasible because of interference with the existing longitudinal beam connection.
C1.3.2 Providing New Diagonal Bracing Assume that diagonal bracing is to be considered for the longitudinal direction of the building. If the existing diaphragms have adequate capacity, the new bracing can be located in the exterior walls to avoid possible interference with the internal circulation within the building. If the diaphragm has inadequate capacity to transfer 
186 
the seismic shears to the exterior longitudinal walls, it probably would be more cost-effective to brace one or more of the interior longitudinal frames rather than to strengthen the diaphragm.
In the design of the vertical bracing, X-bracing will be more effective than diagonal or chevron bracing for most braced bays because the tension diagonal will provide lateral support for the compression diagonal. Many designers assume that the effective length of the compression diagonal for X-bracing may be taken as one-half of the diagonal length for the in-plane direction and two-thirds of the diagonal length for the out-of-plane direction. Since the greater L/ will govern the capacity of the brace, this leads to the use of brace members with different radii of gyration, r, about each axis.
The number of braced bays must be adequate to resist the story shears; however, in this building the story shears are not severe and can easily be resisted with only a fraction of the number of bays available in the exterior longitudinal frames. Next, the existing columns and foundations must be investigated for the overturning loads in the bracing. If it is assumed that all braces are equally loaded, it should be noted that with multiple contiguous bays of X-bracing there are no additional vertical forces in the columns and foundations except at the extreme ends of the braced bays. Therefore, if the existing columns or foundations do not have adequate capacity for the calculated overturning loads in the bracing, the engineer may be able to reduce these loads to acceptable limits by using smaller brace members and increasing the number of braced bays. The required structural modifications (Figure C1.3.2) involve: 
1. Removal of the existing concrete fill and steel (E) column decking at second floor VP and roof levels to permit welding of gusset plate to (E) beam shear beam flange. Since the connection gusset is to be welded along the center of the (E) floor beam flange, only a narrow section of decking needs to be removed.
Care must be taken that adequate bearing remains (N) gusset plate for the decking.
2. Welding of gusset plates to the beam/column joints and to the column/base plate joints. (N) X-bracing 3. Welding of new diagonal braces to the gusset plates.
The design of the new plate A' w e n bracing system must include a e ()tension structural investigation of the to base plate ad
of the existing provide
I additional
capacity of the existing co-' anchor bolts, as, beams, and foundations A required to resist the additional forces associated with the new FIGURE C1.3.2 Providing new diagonal bracing to an existing steel frame. It should be noted that the floor beams in the braced frames are required to function as collector members to "collect" the diaphragm shears and distribute them to the braced bays. The beam-to-column connection must therefore be capable of transferring tensile or compressive forces as well as resisting the vertical reaction of the floor beams.
187 
C133 Providing New Shear Walls New shear walls of reinforced concrete or reinforced masonry may be provided in lieu of bracing or frame action in either direction of the building. If shear walls are provided, they should be infilled bays on a column line and preferably in a location where window or door openings are not required. With infill walls, the columns can function as boundary members for overturning loads and the beams or girders as collector members for the shear walls. The shear walls probably will require new foundations and also will add significantly to the building mass, which will increase the seismic story shears.
CIA RELATIVE MERITS OF THE ALTERNATIVE STRENGTHENING TECHNIQUES As indicated above, the frame columns have inadequate capacity to resist the seismic story shears in the longitudinal direction; therefore, new vertical bracing or shear walls are the available options. It appears that the bracing could be installed in the exterior longitudinal frames without strengthening the columns or the foundations whereas the shear walls probably would need new foundations and be more disruptive as well as requiring more time for construction.
In the transverse direction, providing moment capacity to the existing frames (Figure C1.3.1) appears to be feasible. It appears that this would be required for about two-thirds of the frames in the transverse direction at the second floor level and only about one-half of the frames at the roof level.
Preliminary design of the structural strengthening concepts should be performed to define the location and extent of the modifications and to size the new structural members. Relative costs for the various alternatives also should be developed and attention should be given to the other considerations described at the beginning of Chapter 3. With this information, the most appropriate seismic strengthening technique for the building can be selected.
C2 UNREINFORCED MASONRY BUILDING EXAMPLE C2.1 DESCRIPFTIONOF BUILDING This building is a two-story structure, 30 ft by 100 ft in plan. The first level has an open front at the east end and a longitudinal bearing wall on the centerline of the building. There are no crosswalls in the first level, but the second level contains apartments with many crosswalls. The roof diaphragm is constructed of diagonal timber sheathing. The floor contains finished wood flooring over timber diagonal sheathing. The existing conditions are shown in Figure C2.1.
C22 DEFICIENCIES The building's deficiencies involve: 1.
Torsion--The east end of the building has negligible resistance to lateral loads at the first level and constitutes a severe seismic hazard.
2. Adjacent Building--The adjacent building on the south side is not separated from the south wall and would act as a buttress for the diaphragms of the subject building. This could result in damage to both buildings.
3. Wall Stability--The gabled east and west walls at the second level are too slender (i.e., 9 in.) for the calculated out-of-plane seismic response imparted by the roof diaphragm.
4. Wall Anchorage--There is a serious inadequacy in the anchorage of all walls to the floor and roof diaphragms.
188 
5. In-Plane Shear Strength of Walls--In addition to the obvious deficiency in the open east wall at the first level, there also are potential deficiencies in the remaining east and west walls at both levels.
6. Parapet--The 9-in. unreinforced masonry walls in the second level terminate in an unsupported 18-in. high parapet above the roof level that may be a hazard to life safety in a severe earthquake.
SECOND LEVEL
13-inch masonry
exterior walls N I,
9-inch masonry : t-partition A._; FIRST LEVEL FIGURE C2.1 Existing two-story unreinforced masonry building.
C23 STRENGTHENING TECHNIQUES The structural evaluation of this building was conducted using the ABK Methodology for unreinforced masonry bracing wall buildings with wood diaphragms. The recommended strengthening techniques (Figure C2.3) also follow that methodology.
C23.1 Torsion The east wall of the building is deficient in both strength and stiffness. In addition, extensive wall anchors are required at both the first and second levels. Although the open front condition at the first level could be improved with either a concrete or steel moment frame, the extensive additional work required for this wall and its foundation combine to make replacement an attractive alternative.
189 
Replacement of the existing east wall with a two-story reinforced concrete frame is the recommended strengthening alternative. Since the roof and second floor joists are supported on the longitudinal walls, shoring will not be required as the east wall is removed. Temporary lateral bracing in the north-south direction should be utilized during the replacement of the east wall. The new (N) 4-inchl reinforced n (N) wall anchorages second level wall would be a concrete overlay at second and roof metal stud wall with window on (E) wall (E) wall levels levels > openings similar to the existing ones and with brick veneer to F I [II fill I I1 I match the other brick walls, desired.
I C2.3.2 Adjacent Building The proposed solution to the problem with the adjacent
(N) reinforced concrete building is to provide a new
frame with brick veneer>/ reinforced concrete shear wall on steel studs --in the first level of the subject SECOND LEVEL building. The wall would be in line with the west wall of the (N) plywood sheathed (N) reinforced adjacent building. In addition crosswalls concrete frame to the new shear wall, three new timber cross walls will be provided in the first level (Figure C2.3) to reduce the diaphragm deflection. The shear wall, the cross walls, and their connections to the floor diaphragm will be designed in accordance with the ABK Methodology. This strengthening reinforced concrete may not completely solve shear wall the adjacent building problem, but the new shear wall and the FIRST LEVEL cross walls will significantly reduce the inertia forces transmitted
FIGURE C2.3 Proposed structural modifications to the adjacent building.
C233 Wall Stability The height to thickness ratio, h/t, of an unreinforced masonry wall is used as an index of the stability of the wall for the out-of-plane seismic response induced by the diaphragm. The east wall is to be replaced with a reinforced concrete wall so that the west wall in the second level is the only remaining wall with an excessive h/t ratio. The deficiency can be corrected by providing anchors at the ceiling level and bracing this anchorage up to the wood diaphragm or by designing vertical wall braces that span from the floor to the roof anchorage level.
190 
C23A Wall Anchorage All anchorages of masonry walls to diaphragms were found to be inadequate at both levels of the building.
Supplementary anchors must be provided for the calculated anchorage. The anchors should be similar to those indicated in Figure 3.7.1.4a or b. Significantly greater allowable loads are permitted for anchors that extend through the masonry wall with a large metal washer on the outside of the wall. This type of anchor should be used in all locations where access is available to the outside face of the wall.
C2.3.5 In-Plane Shear Stress The new reinforced concrete frame at the east wall, the new shear wall, and the new concrete overlay for the west wall at second level have eliminated the calculated in-plane overstress in the east and west walls.
C2.3.6 Parapet The unreinforced and unbraced parapet is a life safety hazard because of its h/t ratio. It is recommended that the parapet be reduced in height by the removal of several courses of brick (i.e., 8 to 10 in.). This should be preceded by a horizontal saw cut at a mortar joint on both sides of the wall to avoid damage to the remaining brickwork. The top of the reduced parapet then should be sealed with a mortar cap to prevent intrusions of moisture into the wall.
191