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MISSOURI DIVISION |
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PROCEEDINGS OF THE SEPTEMBER 2000 POST EARTHQUAKE HIGHWAY RESPONSE AND RECOVERY SEMINAR HELD IN ST. LOUIS MISSOURI
RESPONSE TO HUMBOLT & LOMA TRIETA QUAKE BY EROL KASLON
ED GRAY: Good morning. Our next speaker is Erol Kaslan who serves as the Senior Bridge Engineer and Branch Chief for the Division of Structural Maintenance and Investigations of the California Department of Transportation. He supervises an engineering section that is responsible for performing NBIS bridge investigations and providing bridge maintenance recommendations on about 4000 bridges in 13 counties. He's a member of the CALTRANS Underwater Investigations Dive Team.
He has performed construction related repairs and temporary shoring for damaged bridges in the 1989 Loma Prieta earthquake. He worked in the 1992 Humboldt earthquake and was field team leader for bridge assessment efforts following the 1994 Northridge earthquake.
Mr. Kaslan holds a BS in civil engineering and a MS in structural engineering from University of California, Berkeley. He´s also a registered civil engineer for the State of California.
EROL KASLAN: I´m a senior bridge engineer working for the California Department of Transportation in the Office of Structure, Maintenance, and Investigations. It is actually now called the Division of Structure Maintenance and Investigation. I will speak on the bridge damage assessment efforts that followed 1994 Northridge earthquake, as I was the field team leader for that project.
I work under the auspice of the Engineering Service Center is the Division of Structures, formerly the Bridge Department. The Bridge Department is roughly responsible for the design, construction, and maintenance of our state bridge inventory.
We're the office in CALTRANS responsible for performing all the NBI bridge inspections and the biannual bridge inspections statewide, including most of the local agencies in California. There are only about a half a dozen cities and counties that do their own.
We're the lead office in the department for bridge damage assessment. We coordinate and perform damage inspection and repair activities for the Division of Structures. We make recommendations for repairs that are designed, administered, and constructed by other offices in the division.
The Northridge earthquake occurred on January 17, 1994, about 4:30 in the morning on the Martin Luther King holiday. The epicenter was about a mile southwest of the city of Northridge or about 25 miles northwest of downtown LA. The magnitude was said to be anywhere from 6.6 to 6.8. It was the real shaker with peak accelerations of about 1.8 lateral and about 1.2 vertical. It was a real rumbler. There were numerous aftershocks in the days following the earthquake. Many of them were 5.0 or better. For those of you who are interested, it was a blind thrust fault rupturing about three miles beneath the surface. It's significant in that no one really knew it was there before.
There was widespread damage that occurred from the epicenter of the earthquake all the way to downtown LA with many areas of localized heavy damage.
The first day I got called at 5:30 in the morning by my supervisor who said there was an earthquake in LA. He didn't know very much but he thought it would be a good idea if I were to come into the office anyway. I kind of grumbled about it, got up and got showered to go in. My wife suggested, well, why don't you pack a bag. As it turns out, that was pretty good advice because I didn't return home for about two weeks. I got to the office about 6:30. By that time most of the senior and supervisory staff had assembled there with a few of our bridge maintenance engineers.
For the first couple of hours, details were real sketchy. There were news reports on the radio of highway damage and some television reports. It was pretty dark down there still. It was mid January and the sun hadn't come up yet. We didn't have a television in the office. It seemed to be the guys in the helicopters who could tell us the most. We had a tiny handheld portable TV with a two-inch screen. We were all clustered around that.
I'll never forget when we first saw the collapsed 5/14 Interchange. It just went silent in the office. Phones were out through most of LA. We couldn't get a phone call in or out down there in our southern office. The lack of information through those first hours was pretty widespread.
We have a satellite maintenance office down in Los Angeles that was responsible for those areas south of Tehachapi Mountains. We tried calling them at the office and at home. There were no phones and no reports were coming into headquarters from District 7.
Power and communications really did remain out there and information was very sketchy for most of the first day. But within a couple hours, we had confirmed reports of heavily damaged highway bridges. We had seen it on TV and finally got a call from headquarters. With that, we began mobilization to get staff down to Los Angeles to assist in the assessment efforts. That happened by about 10:30 in the morning. By 9:00 o'clock or so, most of our maintenance staff or maintenance engineers were in the office and we were preparing to mobilize. About 200 design and seismic engineers working in the Division of Structures just showed up. We didn't call them. They just heard about the earthquake, came on into the office, and started milling around. They asked if there was anything to do. We just wrote their names down on a white board. So when it came time go down there, we would have a written pool of talent to draw from.
We began our mobilization efforts by forming two-person teams to inspect the damage. We figured that we could link up one of our experienced field maintenance engineers that are used to looking at damaged bridges and a variety of different structure types with a design and seismic engineer. We thought this would provide a good balance between feet on the ground experience and theoretical background familiar with modern seismic designs.
We equipped all our teams with cell phones and four-wheel drive vehicles. In 1994 we had two cell phones in the whole office and you had to pretty much pull teeth to get a hold of one of them. That morning they were showing up by the box load.
Mobilization of the whole department really came to light in getting the vehicles out of the shop. Most of our guys put their vehicles in the shop for the long weekend to get them serviced. That Monday morning, the shop superintendent showed up in his undershirt and just unlocked the door and rolled all the vehicles out. We mobilized all of our resources pretty quickly.
We supplied everybody with an assortment of common inspection tools, basically hand tools that any one of you would use to perform routine bridge inspection; cameras, etc. There were no laptop computers in those days, no electronic devices, nothing.
The initial instructions were to just head on down there. Sacramento is about 375 miles from Los Angeles and about a six-hour run. We instructed the guys to fuel up, put some water in their car, get their basic supplies, and get moving. About halfway down that journey, everybody was independently moving in their Chevy Blazers. Cell phones were going off. We had instructions to rendezvous in Bakersfield about hundred miles north of Los Angeles at a maintenance station to receive further instructions about where to go and what to do.
As it turns out, when we got there, the grapevine, that is I-5 passing over Tehachapi Mountains into Los Angeles, was reported as heavily damaged and impassable in some areas. We were instructed to meet up with a California Highway Patrol escort who was going to take us up and over the grapevine and into the damaged areas. It was really quite a sight to see. The freeway system down there was shut down and we had this long convoy of 15 jeeps and a couple of big orange trucks led by the police in front and back.
On the first day when we were mobilizing from Sacramento, the local Los Angeles based maintenance and construction crews did sporadic damage assessment. Those efforts focused on the most heavily damaged areas: collapsed bridges. That is normal. That tends to get the most attention. There had been no systematic investigative or recording efforts started. Major portions of the entire system down there were closed. If you can imagine a freeway system in LA being absolutely barren of cars, that's what it was like.
Of course, everybody was staying home, as we really couldn't open the system without knowing what was safe and what wasn't. We had areas of damage that were separated by 25 miles. So we really had reason to look at every single bridge in a large radius around the epicenter.
A systematic approach to do that was required. What we needed to do was thoroughly cover the effected areas so we could reopen the system as quickly as possible. Our investigative teams were given a route assignment. That is, take this highway from this milepost to this milepost and the basic instructions were to look at the bridges. If you see something that was going to fall down and hurt someone, stop and provide shoring or other closure efforts as required. Then, write a comprehensive report of what you see even if it was a no-damage scene. A bridge inspection without a bridge report in these efforts is really useless. We found that many guys had gone out and local crews had gone out and said we looked at that bridge. There was no way of ever knowing that because they never wrote anything down or let anybody know.
The work begins on that first morning. We provided our teams with maps of the LA area. We were all from Northern California and you can get lost pretty easily down there so we got maps for everybody. We used our bridge logs, our little inventory of bridges by milepost and bridge number. Unfortunately, we had no plans or previous bridge inspection reports for the structures down there: some 2,200 in the area. That's where the bridge maintenance engineer experience really showed. We had been looking at similar structure types throughout Northern California and certainly could tell what was right and what was not right for similar types of bridges in LA.
The systematic inspections began that Tuesday. Our workday usually started at daylight and stopped at dusk. We started our day with a 5:30 breakfast at the hotel in Pasadena that was outside the effected area. We had a mandatory 6:00 o'clock meeting in which we were to go over route assignments and update information and reassign teams as required.
By the second day, additional resources from throughout California and Nevada began to arrive. We had four district bridge crews from Districts 2 and 3 from the northern most portions of the state and a local crew from District 7.
Both of our CALTRANS snooper trucks showed up on site without anybody really asking them to. The Nevada DOT graciously supplied us with their reach-all UB50 and it was a fantastic asset to have.
Our Transportation Laboratory and Materials Group sent their fractural critical and inspection team. These guys are used to looking at fractured critical steel bridges. At the last minute, one of them brought a boroscope. Do you guys know what a boroscope is? It's a little camera mounted on a flexible tube. I guess the medical industry uses them to stick inside your body and look around. We thought he was pretty silly for bringing that. It turned out to be a very valuable tool.
By that time we had a basic framework of headquarters, command and control, and support staff established.
As we began the inspection efforts, each team went out on their way and certainly every team saw different things. Some saw very little or no damage at all for their entire stay down there. Some saw severe damage almost immediately and that grounded their efforts to a halt and commanded their attention for their entire stay.
There were different levels of damage in different areas. Consequently, almost on a daily, and some cases an hourly basis, we had to rotate and reassign teams to make sure we could cover those heavily damaged areas.
Bridge damage assessment is really not always easy. I've always said a bridge collapse is the easiest one to assess. The bridge is collapsed; it's down; it's no good. The intermediate damage was a lot more difficult. Routinely, the teams would be looking at bridges that exhibited what would appear to be moderate to heavy damage and had to answer a lot of serious questions on the spot. Can the bridge still stand up? Is it a stable structure? If it could stand up, does it have any reasonable safe load capacity, or could it be put back into some level of service for emergency service to full highway capacity?
You know, these decisions really were judgment-based decisions and this is where the team effort of two engineers on site -- one maintenance engineer and one design engineer -- really worked out well. We required that each team had to reach consensus on their opinion of the bridge before the report was actually generated.
Well, the daily inspection routine, for you guys that are used to getting up and going to work, that's kind of what it evolved into. I mean it was a fantastic project but yet everybody had to get up and go to work. We all stayed at the same hotel. It was a Double Tree in Pasadena, a real nice place. Breakfast at 5:30 and a meeting at 6:00 o'clock. Those meetings became crucial for updates of information and reassignments.
Then we would go out at first light of day by 7:00, 7:15 and inspect bridges all day long. We were calling in and out almost on the hour for updates and information. That's when the cellular phones that showed up in mass the first day we mobilized proved to be the most reliable means of communications.
We had radios in the cars. We had all kinds of stuff to use. The radios were absolutely ineffective. The repeaters were just not working for us. Of course, you move from one area to another, it would be a different system and a different set-up and different protocol and the airways were swamped anyway.
The cell phones, they didn't work every single time, but they worked two out of three. As the days passed by, the cellular companies moved in portable towers and set up them all over the place to supplement the communication system. They really merged as being the most reliable means of communication. I think my cell phone bill for the 14 days I was there was around $1,900.
We would inspect bridges all day, return to the hotel, meet in the lobby by 6:00 o'clock. If you didn't show up or let us know where you were by 7:00, we assumed you were missing and sent the highway patrol out to look for you, but only one guy did that.
At that time we were required to collect all the reports, provide any new assignments, and update the information. Things were getting better and better, as time went on. In the evening was our time to relax and exchange experiences. A lot of guys, including myself, were certainly seeing things we had never seen before. We inundate the hotel bar. You can imagine a group of 35 engineers just buzzing about shear columns, broken bearings and all that stuff. It was really something else. By that time of day, it was the only time you had to yourself to take a shower, get cleaned up, have a decent meal, and relax a little bit.
Sometimes during the day, it would get highly stressful not only looking at the damage but dealing with the other crews, local police, fire, and certainly the politics coming down from above redirecting our work. All that would keep you wound pretty tight.
I'll elaborate on damage reports a little bit. The flow of information was absolutely crucial. That was hammered into my ear from the moment I left Sacramento. Keeping the information pipeline open and keep the information flowing.
Damage reports were collected at the end of every day. These were handwritten reports done by pencil in the field. Some of the guys completed them in the lobby at 6:00 o'clock. They contained the information as to the type, location, and extent of damage, as well as a rough repair cost estimate and other relative details.
Federal Highways and FEMA, were asking everyday, "How much is it going to cost? We had faxed from headquarters a rough estimating guide based on construction statistics. Within a few days, we all became pretty good spot estimators of bridge damage. The reports were collected and taken to a central office that was set up in an undamaged section of Los Angeles. That's where the clerical staff stayed up all night and typed the reports, made them legible, and entered any relative data into the database. These were the days before local area networks and fiber optics so the databases were kept in the office. Throughout the night and early morning hours, we sent the data by courier to headquarters and local offices.
The bridge damage reports are pretty crucial. They contain the critical information that everybody wants to know. An inspection doesn't mean very much without a comprehensive report to back it up, even if it was a no-damage report. It's the root document from everything to dollars, to systematic management, to earthquake research years on down the line. We really had to stress to the guys, you're going to see a lot; it's going to take a lot of effort, but write it down and be a pro about it.
Many entities really required the information hourly. Federal, state and local levels, there would be times I had to stop everything and gather up the guys, get their reports and actually hand it to a courier and send the information in. But keeping that pipeline flowing was very critical.
We were working and production was certainly stressed. We couldn't just grind to a halt. We had teams up there performing a job covering some 2,200 bridges as quickly as possible. So rapid assessments were required. We were asking the guys to don't write down every single crack. You're going to look for the big basics here.
We also thought it was important that the teams learn from the experience. So those crews that were in the least damaged areas, sometimes we'd switch them out, and rotate them to more heavily damaged area so they could get that experience of assessing earthquake damaged bridges.
Aftershocks were occurring throughout those days. Many times we'd have to go inspect the same structure again and again and again. Certainly one of my most memorable experiences was on the 210-overpass separation. There's a big old long connector structure. I had one foot on one side of the hinge and one foot on the other side of the hinge when a 5.2 after shock occurred. I tell you, there was two independent three-dimensional degree of movement going there. It felt like I was in two rowboats. That was a pretty exciting experience.
Our teams worked pretty well together and really contributed to the acceptable production rates that we were achieving out there. The guys were hitting about 10 to 20 bridges a day. The reason being is that between you and the crew, you can pretty much figure out very quickly what was right and what was wrong and put it down on paper.
The varied experience levels and opinions and areas of expertise really meshed very well. The judgments that the guys made in the field turned out to be fairly accurate on down the line. Within the first six days, we had investigated over 800 bridges in the effected area and submitted over 550 completed damage reports. We were really cranking it there.
California has a large majority of box girder bridges, both reinforced concrete and prestressed concrete. A lot of these, along the connectors, contain an intermediate hinge, thermal expansion. Of course, those are the weak spots on the bridge as the two frames can shake at different times and the hinges can become unseated causing a partial collapse or pre-collapse of the bridge. Our primary measure is to either put restrainer cables or pipes in these hinges to hold the bridge together while still allowing for thermal movement. We can look at these hinges from the outside and we could tell that something wasn't right. It was evident there was spalling, cracking, and lots of evidence of movement. But the interior damage to these hinges, those parts of the bridge on the inside, we couldn't access them very easily.
We really concentrated on dead load, live load capacity of the bridges. On this one here, it was a little different because of all the aftershocks.
California did not, until very recently, provide an access opening to the interiors of the box girders. I encourage any bridge designer doing a box girder to put one in every cell, whether you think you need it or not.
So consequently, on those bridges where we had to find the cell and we had to chip a manhole to death around the hinge. If you've tried to go in a bridge deck around a hinge with all that steel, it might be several hours to get a one-by-one manhole through the deck.
Our initial investigations had focused on load capacity. We really didn't know from the inventory down there what lateral or longitudinal capacity remained. We kept phoning this into the office. It was a heated topic of every evening beer discussion. We phoned it into the office. Finally on Day 6, which was a Sunday in the morning, the Division Consensus in Sacramento said, we weren't going to open any bridge that we didn't feel had the lateral or longitudinal strength and couldn't withstand an aftershock. Therefore, we must determine the condition of all our hinge restrainers and other components to resist seismic forces.
Unbeknownst to the headquarters in Sacramento, District 7 had planned on opening 5/14 Interchange that following Monday morning for commuter traffic. They had dozed a road down through the damaged portions and removed the collapsed bridges. They really had things going gangbusters. They were going right underneath what was left remaining of this interchange. There were lots hinges and lots of bridges still up in the air.
I'll never forget standing in front of the district construction deputy and telling him, no, you can't do that tomorrow. Of course he told me we're doing it anyway. Consequently, we diverted most of the teams to the interchange to perform these inspections. It was seven engineer teams, all three-bridge crews, all three snoopers, and various, visual-inspection equipment. We had pole- mounted video cameras; we had weep holes in these box girders. We found a little camera that was made for inspecting holes. We stuck it on a pole and stuck it up in there. With a light source were able to visualize a lot of what we couldn't see.
We used the boroscope, that little fiber optic camera, to look inside the cells. Those turned out to be pretty good. We drilled a little half-inch hole in the bridge deck and that took about five minutes. We stuck the boroscope in and took a look. We were able to see enough to say either good or no good. Those emerged to be a pretty good tool. When we figured that out, we had the vendor come out and he sold us two out of the back of his Toyota Celica on the bridge for about $11,000 a piece.
During the night, those restrainers that we found were damaged. We repaired them and switched from being bridge inspection engineers, back to being bridge maintenance engineers. Some members of our team got together and designed a replacement restraint system with a bunch of heavy duty deck bar lying around the maintenance yard. We were able to get our bridge crews to install them. Consequently, that interchange opened on time on Monday morning.
That started us into a real effort of looking inside bridges. You've got to understand that when you do these damage assessments, you'll do a lot of visual investigations. You have to look deeper into the structures and it's going to require a lot more time and resources than you initially think.
The hinge inspections for us were greatly hampered by the inability to see inside the boxes. We even had a World War I artillery periscope that they used to use in the trenches. Somebody dug one up and we'd stick in the weep holes. The high-resolution, 11-millimeter boroscopes were like gold.
By this time, the pressure was on to reopen the entire system. So those bridges we looked at initially for dead load, live load and determined they were okay, we had to go back into them and close them down to traffic, get the snoopers on them, and get in there to take a look at those hinges. Our production rate dropped way, way down and there wasn't much we could do about it.
But certainly by the eighth, ninth, tenth day, the initial damage assessment started winding down, things became routine. The total damage assessment effort lasted about three weeks. The initial damage assessment was pretty much completed in the first ten days.
We had a good snapshot of what needed to be done in the second phase. By that time, our design and construction engineers began arriving from all over the state. These guys were armed with plans and open contracts to start demolition and rebuild. Bridge contractors were just showing up all over the place. They were really in full mobilization. False work and shoring were showing up by the truckload and there was truck after truck of timber. The demolition contractors were pulling in most of their equipment from Washington, Oregon, Nevada, Arizona, and repairs and reconstruction were already in full tilt on a couple interchanges.
So by that time, most of our investigation teams were called to Sacramento. Four teams were left behind in the field to finish up the work.
So concluding this part of it, just to say we were able to investigate 1,500 bridges and create 760 comprehensive damage reports within the first two weeks. None of our teams reported any injuries outside of a lot of sore feet. The assessment teams worked very well. I can't begin to stress how having two engineers in the field with different backgrounds really contributed a lot to these judgment-based decisions that were made.
In the earthquake, five bridges flat out collapsed and hit the ground. Four other bridges had major damage but and didn't collapse. They required demolition and reconstruction. Most of the other bridge damage we saw was minor to moderate. So it was a real good learning experience for everybody on our staff.
Well, I started out here with most of the common damage that was reported to our teams. We got calls of heavy highway damage from the CHP, the fire department, and concerned citizens. We'd hustle out to these bridges. In both earthquakes that I've worked, the most common form of highway damage was the approach fill. It was where the approach fills on either side of the bridge abutments itself. The bridge would rock back and forth and consolidate the fill behind the abutment. In some cases, these things would settle out several inches. We were ramping up quite a bit on these bridges. We would go out and look for heavy damage and go, oh, this is just approach damage, and be able to move on.
Some of the settlements were really enough to render the system useless because they were six to eight-inches tall. You really couldn't traverse the bridge. So there was a lot of this going on within the right-of-way. I don't know how many hundreds of tons of AC were placed but that was happening all over the system. If you go down to LA today and you drive around, you'll see the remnants of these AC ramps all over the place. They worked okay and they're still holding up.
Other common damage that we saw on just about every bridge was bearing damage. Our late 1950s and early 1960s reinforced concrete boxes had just a plain steel bar rocker with a keeper plate and keeper bolts. Just about every one of those we looked at, at least one of the bolts was sheared off, if not all of them. Even if there was no other seismic movement or damage on the bridge, those bearings were pretty darn weak.
The Mereck bearing was one of our more common bearings. For this one it sheared completely over, pealed off, and rolled over to where we had a little abutment. Abutment damage was pretty common. Bridges would rock back and forth. You can see damage like this. This is just located on the front of the abutment. That would give us an indication that the bridge had moved. You can look at the basic superstructure and substructure and not see any damage, and tell it really took a rock by looking at these other portions here. Some separation of the sloping there would give way. Wing wall separations were pretty common. The wing walls on a lot of our bridges are independent from the abutment. We could see where the wing wall went one way and the abutment went another and a big gap.
The public and local police department would call in and report a huge crack on the bridge because, of course, you know they're used to seeing no gap. Now this thing looks like a huge crack to the untrained eye. So that kept us pretty busy for a while just running down that.
We saw a little more substantial abutment damage. On this one you can see some minor spalling, continuous No. 10 and No. 11 bars where the superstructure actually rocked against the diaphragm abutment.
On the more modern bridge designs, we have these transverse shear keys. When you get up close, you can see where it certainly worked. We´ve since learned this is a bad detail. You know, it's effective in restraining transverse movement but you can't get in this and fix it very easily. So we've kind of abandoned these internal shear keys on a more modern designs.
External shear keys, certainly they were doing their job. There's a neat 45-degree shear crack on the external part of the box girder or the abutment.
In some cases, the abutment had actually started to come apart and separate with full depth cracking. Not really quite sure why. Perhaps it was a different slope condition or different foundation type. One pile to a next would be a little bit different stiffness. But nonetheless, we started seeing these abutments crack up. They were good for dead load, live load, and could reach a fairly good seismic load level.
Here's another example of a bridge that actually rocked pretty good on its diaphragm abutment causing a lot of spalling and exposed bar here. None of these bars were buckled. At least a team on site figured, they rocked back and forth and they yielded and they might have stressed a little bit but they were still back in shape and they were working. We consequently scratched that stuff up and kept going.
Moving to column damage. It's pretty much our investigative sequence of looking. You start by looking at the approaches. You get under and you look at columns and then the bearings. You work your way from the ground up to the superstructure. The superstructure is fairly tough. But the substructures were really the vulnerable points. It´s the column damage. Even though you look at a column and the physical element didn't have anything to see in the ground around it, you can tell the thing really rolled around a little bit. We were seeing earth displacements and earth cracking on a lot of structures. It was evident that it had rolled around but left no other seismic damage on the bridge. I remember this from the Humboldt earthquake as well.
On some the whole pile cap rocked back and forth. In some cases, we see just very minor evidence of movement. An internal drain was just sheared off and separated.
Once you start looking down, you're going to start looking up. We saw a lot of minor spalling at the top of columns where we inspect the plastic hinge form. We looked at these, and said, okay, yes, it rolled around a little bit, but it was still hanging in there and it was good. We go back and take a look a spall column after an aftershock and one of the bars had been buckled either on spall or kind of increase longitudinal length of the bar. Then we'd get another aftershock and we'd get something like this. So these bridges get softer. Every time they take a hit, they would get a little bit softer, even though the aftershocks were minor. A bridge that was open, one over 34, I looked at five times. By the fifth time, we had to close it and shore it up. It was open to full traffic for several days. We had to go back and close it due to the aftershock damage. It was kind of a big deal.
We've got this nice long monolithic column. It´s intended to be fixed on the bottom. It was encased in a Jersey barrier around the median, and it changed the location of the plastic hinge. It changes the stiffness of the column. It's a much shorter column than was designed. None of the rest of this particular structure showed any damage. This column had some significant cracking. We believe it was due to the casement in this median barrier. We don't do this anymore.
This is where the engineering team worked out real well. A routine bridge inspector might know heavy cracking and keep this bridge closed. But if we look at columns like this and look inside, we´d be looking for a nice clean, unconfined core. The cover does fall off and the core does remain intact in many cases. It looks bad to the untrained eye but to the design and seismic engineer, it's beautiful. It worked. So we just patch this up and move on.
In some cases, we could see the hinging fork inside the core. We´ve got a couple separated hoops. These get a little bit trickier depending on structure type, where the pins were intended to be, and how many columns. For vertical loads only, this is pretty good. For lateral loads, it gets a little trickier. Certainly, if we were seeing this plastic hinge and a core full of rubble, we would elect to go with false work and shoring for lateral loads.
Here's an example of a full bent that was taken out. I remember seeing pictures of this when I was in college. It´s a nice, neat shear crack, spiraling around that column. The hoop spacing is again at 18 inches. These are round columns with very heavy reinforcement bars around the circumference but really no confinement. On this particular bent one of the columns had no damage. The other one sheared off; a textbook example of shear failure. We were probably just a couple of seconds from this thing blowing up. There really is no confinement to that column. Some of the others did pretty well. When you look at Bent 5 columns, they're all the same. Why would one of them get it and the rest of them not? Why would three of them get it and one of them remain whole? Everybody had a great opinion on that.
This is what some Northridge columns looked like at another bent on a bridge where they did get another couple seconds of shaking. It absolutely blew up. Here we got one that would hinge at the bottom, one that would hinge on top. Why would that happen? I´m still trying to figure that out. Of course, I have to show the spectacular mushroom failure. The chunks of concrete in there were as big as Volkswagens. Look at all those twisted No. 11 bars. We see it mushroomed out at the bottom. In some cases, they mushroomed out and fall down at the top. Heavy column damage was the weak link in these bridges. Here´s a close-up of every single one sheared off right where they weren't designed to at all. It´s pretty spectacular damage.
We had emergency vehicles running over this bridge. It settled down but right on its haunches and right on a big old piece of rubble. So the fire trucks and our vehicles were going over it. This one we eventually had to demolish and replace.
California loved these one-way flares on columns. When I started out in bridge design, we put these flares up here but they´re really ineffective to the stiffness of the column. The reason being is we like to reinforce relative to the confined core of No. 7 bars. Widely assumed on the design core that these things in a seismic event would just simply fall right off. The failures on these flared columns occurred right at the general stiffness change. There was some tight spiral but still that stiffness change was too much to bear. The designer had to take into account the flare geometry of the column.
There are the No. 7 bars that I was told were just going to fall right off. We don't do this anymore. You take a look at a modern bridge in California and we still have those flares but there's a nice big gap all the way around the top. Prismatic shape still is the load-bearing portion of the column and this is truly architectural.
That's what a mid-1970s California area box hinge looks like on some of our earlier box girder designs. Very narrow seat about nine inches. The bridge rail is separated and the bridge balanced back with the rail separation, also a little bit of a vertical offset across the bridge rail and some spalling.
This would be what the investigating engineer would run into. He would look and have to determine what was going inside of the box. You look down at the rail over and over again at these hinges and see details where the rail had come apart, shifted one way or the other and slammed back together again. We had no way of knowing if that was in the acceptable range in the restraints system that was inside of these things. The joint seals were all torn up. You see the compression seal where it was separated and not compressed any more, some local spalling of the deck around these hinges where the structure was slamming into itself.
This is parapet damage on the bridge rails. The rails were usually constructed last on the bridges. They had a little bit of a tighter fit. The bridges rocked back and forth on itself. Right on the very exterior of those rails they were smashed up pretty good.
On these hinges, we would get pretty nervous and kept the bridge closed until we could pop a hole in it and see what was going on. In cases like this, we reasoned the thing was barely hanging in there.
The bridge retrofits of poured concrete bolster on either side to give a lot more strength to the entire system here. A double strung pipe or a system of cables through it, either one way or wrap around a drum would hold the hinge together as it took the longitudinal load. That's what we were trying to look. We used a pole camera to look inside. This is what we would see when we got lucky. There's a restrainer with a cable system wrapped around a drum and all of them looked like they were on that side. We had to go in on the other side to see if they were on the other side too.
We'd see the drums out with the cables barely visible. We'd have to do a count; one, two, three, four, okay. I saw this many. How many did you see? It took a couple of tries for everybody to see the same thing looking through the 11-millimeter boroscope. It's not a crystal clear image.
This is an aerial of one of our hinge inspection activities on a connector in Pasadena. We had the snooper trucks hitting every single hinge. Some fracture critical guys with special vehicles were there. After a lot of rigging inspections were done, we had to gang up. We just simply closed down one ramp on the interchange and spend several hours there getting into it.
The 154 Interchange was heavily damaged. A lot of this was easy because it was already on the ground and it was closed. You can see all that rebar was hanging down. You can see box girders are pretty tough but they can't hold up to something like that. You can see some restrainers stuck up in there. They were just overwhelmed by the forces.
If you've ever driven along and wondered what a collapsed bridge looked like, you can tell right a way that something's not right. You can see deflection of a bridge rail. The collapsed one in downtown was eerie. When the fog in the morning is burned off, this is what you saw. It's actually difficult to determine if you were on the collapsed portion or the standing portion. This is what it would looked like from underneath. The superstructure is still in good shape. There was some talk of rebuilding the bent, jacking the thing up, and putting it back in service.We reasoned that it was still within its elastic limits. The superstructure would probably perform well but that was abandoned in lieu of demolition and reconstruction.
This is the Gavin Canyon underpass. I always like this one because that guy's got to be the luckiest truck driver alive. The approaches on both sides are absolutely gone. He's on this table, top frame at a dead stop. He is five feet away from a really bad day.
On the third or fourth days for those bridges that had some heavy column damage, we kept on with the false work and shoring activities. These things were rolling right along and we got this false work all constructed. By this time demolition activities were also well on the way. This is Gavin Canyon. You can see four low ramps on these big excavators taking one of these things down. It kind of looked like a Star War's movie.
I like to point this out because it's the only scour damage I've ever seen on an over-crossing. This was a water main going through the bridge that ruptured during the earthquake and bled off for several hours causing some significant scour damage that we elected to repair.
With the aftershocks, sometimes, you look at your partner and say, "Did you feel that?" Then you'd look up in the distance and see a big old cloud of dust rising up. That's when you knew there was an aftershock. While working you have to be cautious about them.
I took a quick shot of this big old crack running down the center of the I-5 roadway. They just filled it with sealant and paved back over it again, but pretty significant road damage. It was all around as well.
Media parked right in the middle of the activity the whole time. We had to conduct ourselves in a professional manner. If anybody asked us a question and it wasn´t hard to answer, we certainly worked with the media as much as we possibly could.
Do you remember that shot of the bridge in the fog? The CHP was cruising along and he couldn't tell where the collapsed part was. This poor guy eased right over the side.
Thanks very much.
ED GRAY: Thank you, Erol.
AUDIENCE: Would it have been worth your time to have brought a lot of support people along like transcribers and set them up in a hotel so they could voice record all comments and notes and let them work nights filling out the reports?
EROL KASLAN: In those days, that was a pretty new thing to do. In retrospect, we figure we would do that. We would just move in a clerical unit with everything they need to get this transcription and reporting going. Since 1994, we have added a lot of fiber optics around the state so it's actually possible for us to link up with our LAN system.
AUDIENCE: How will your fiber optics system survive?
EROL KASLAN: It´s fairly reliable.
AUDIENCE: What did you do with bridges that had moderate damage? Did you try to close them and shore them up or did you try to post them for certain weight limits?
EROL KASLAN: It really depended on the individual circumstance and the level of damage. But a moderately damaged bridge that appeared to have most of its load capacity intact, we reduced the overall load capacity and put it back in limited service. Where the columns were spalled and we could see the interior core was of an older design and not well confined, we elected to shore all those up.
AUDIENCE: How well did the postings work? Did you have the highway patrol out there?
EROL KASLAN: It actually worked out pretty well. Highway patrol was all over the place. I got pulled over a couple of times. The traveling public was really good about that. I remember inspecting bridges and inspecting an under crossing where I've got a state highway going under a local road, and it occurred to me I hadn't heard anything. Well, I looked and all the traffic on one side was at a dead stop and all the traffic on the other side was at a dead stop. The public they were very compliant.
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