Special Earthquake Insert from the October 1990 Newsletter

quake Investigations Committeeof TCLEE and EERI. Theinvestigation team consisted ofeight members: A Schiff, teamleader, D. Ballantyne, A. Farah,C. Farrar, J. McLaughlin,T.Moore, S. Saxena, and A Tang.The investigation was supportedby TCLEE, EERI, and theNational Center for EarthquakeEngineering Research.

A USGS team of 2 geologists(Bob Sharp and Chris Newhall),2 seismologists (LeifWennerbergand John Bicknell), and 1 geolo-gical engineer ( GelTy Wieczorek)worked with the Philippine Insti-tute of Volcanology and Seismo-logy (PHIVOLCS) from 7/26-8/10 to document the naturalevents and their implications forfuture earthquake risk in thePhilippines and in the UnitedStates. The team gratefullyacknowledges travel supportfrom USAID/OFDA, and fruitfulcollaboration with PHIVOLCS(RS. Punongbayan, Director).

We thank all contributors fortheir response to our request formaterial for this insert to theNewsletter and we thank themcollectively for those photo-graphs we have room to print.

Cojuangco Bridge approaches.

of teleseismic records by theNational Earthquake InfonI1a-tion Center awaits receipt ofbroadband digital records fromadditional stations.

approx1IPately 300 kIn to thesoutheast.

The usual editing efforts havebeen made to avoid too muchduplication internally, and toavoid duplicating material in theEQE report, which is a first-class .publication.

.Up to 5 m of left-Iateraldisplacement occurred along twoadjoining fault segments: a 40kIn long segment of thePhilippine Fault betweenGabaldon and San Jose. NuevaEcija. and a >35 kIn longsegment of the Digdig Fault.splaying north-ward from thePhilippine Fault near San Jose.The northward extent of rupturealong the Digdig Fault is stillunder investigation. with acceSShampered by numerouslandslides.

PRELIMINARY FINDINGS'

I =~S OF 11iE USGS

The team focused on faultrupture. aftershock distributionand character. unusual groundresponse to aftershocks.landslides and liquefaction thatresulted from the mainshock(s).At the time of this writing. digitalseismic data (GEOS) are beingprocessed in Menlo Park whilePHNOLCS teams are continuingfield investigations and study ofanalog seismic records. Analysis

.The greatest damage tobuildings, roads, and bridges

Ioccurred west and northwest ofthe faults. The greatest shakingdamage occurred in Baguio City,where a number of multl-story

.The Philippine Fault is a major .1200-km long. left-lateral strikeslip fault system. A M- 7.7earthquake occurred at 4:26 PMlocal time. July 16. 1990. incentral Luzon. along thePhilippine Fault and a splay ofthat fault known as the DigdigFault. A Japan-Philippinesstudy before this latest eventhad shown geomorphic evidenceof rupture in this area ten-tatlvely correlated with ahistorical event in 1645. In1973. a M-7.3 earthquake

ioccurred along another segmentof the Phlippine Fault.

2

buildings collapsed. We are stillsearching for strong motion

~ records from this and other(', ~arts of Luzon. Liquefaction

occurred locally in lowland areasofTarlac. Pangasinan, and LaUnion provinces. most notablyin Dagupan City and the townsof Agoo and Aringay. InDagupan. some buildings subsi-ded as much as 2 m and tiltedas much as 30. as a result ofliquefaction. Liquefaction alsocaused collapse of the Cam1enBridge on an important north-south artery .near Rosario.Pangasinan. Lateral spreadingor slumping damaged theapproaches and footing of num-erous other bridges. Tens ofthousands of shallow-seatedlandslides occurred in moun-tainous areas. blocking roadaccess to Baguio. the CagayanValley. and many small comrnu-nities. and generally hamperingrehabilitation and recovery fromthe earthquake.

Camlen Bridge liquefaction.

landslides and debris flows havealready occurred. furtherslowing the recovery.

.Was rupture along the Philip-pine Fault relatively slow?Shaking damage was remark-ably slight in the epicentral area.In many places, houses directlyastride the rupture were de-stroyed but neighboring housesand minimally-reinforced con-crete hollow block garden wallswere not.

UNRESOL VED QUES110NS

.Was rupture along the two seg-ments a single or complex event?PHIVOLCS has postulated thatrupture along the PhilippineFault occurred first and wasfollowed by that along the DigdigFault.

{AVO Further damage is expected

from new or reactivatedlandslides. debris flows. andfloods. as monsoon rains andtyphoons hit the areas affectedby the earthquake. Some new

.Why was damage concentratedto the west? Part of the answeris demographic --there isgreater population density anddevelopment to the west. Part isalso related to local conditionsconducive to landslides andliquefaction. However. questionsremain about the extent towhich ground shaking itselfmight have been influenced bymountainous topography. localgeologic conditions. and west -ward propagation of rupture.

~i

I

~~

.Were there significant dif-ferences In ground responsebetween IndMdual buildingsites?

~

.What control, in detail, didseismic amplification, topogra -phy and local site geology haveon the distqbution of landslidingand liquefaction?

Cannen Bridge liquefaction.

3

bridge crosses the waterway; theremaining portion is over theadjacent flood plane.

8SmUCTURALDAMAGE

Throughout the areas visitedthere was an unusual degree ofunifonnity in the construction ofdifferent types of buildings, fromschools, hospitals, officebuildings, hotels and residentialstructures. The vast majority ofthe structures consisted of rein-forced concrete beam columnframes, typically designed asnon-ductile moment frames.They were designed according tothe Uniform Building Code,which is the same building codeas used in California.

Magsaysay Bridge (Dugapan) liquefaction and spreading.

BRIDGE FAILURES

. 1

)

In Baguio and other cities closeto the epicenter such as Agooand Naguilian structural damagewas associated with groundshaking with a large verticalcomponent although there areno strong motion records. InBaguio 28 buildings wereseverely damaged and severalmodern hotels collapsed. InDagupan structural damage wasassociated with foundationfailures due to liquefaction.

Damage to transportationsystems and the disruption tocommunications had a signifi-cant impact on the emergencyresponse and recovery from theearthquake. The loss of roads inmountainous regions and theloss of bridges due to liquefac-tion isolated Baguio for fourdays, and one month after theearthquake only one road isopen to Baguio. All groundtraffic to the northeastem part ofLuzon was restricted to a singlebridge.

Soil conditions may havecontributed to several of thefailures: however. severalfactors may have contributeddamage and failures.

1

j

The Magsaysay bridge on NorthRoad in downtown Dagupan isone of the two main bridges overa major river that flows throughthe city .Two of the six bridgepiers subsided. toppling four ofthe seven spans. The other piershave all tipped and are out ofalignment. Both abutmentssustained severe damage as theapproach fills flowed toward theriver. Emergency measures atthis site consisted of theconstruction of wooden stepsand ramps across the collapsedspans. This facilitated pedes-trian traffic across the river.

~

,CanI1en Bridge liquefaction.

4

The Cannen Bridge on Rt.3between Santo Tomas and SanManual, is almost a mile long. Itconsists of 13 steel truss spans,six of which collapsed. Damagesustained to this bridge was intwo fonns. Many of the rockerbearings supporting the spanswere shaken out from under thespans, dropping the ends of thespans down, and forming stepsin the roadway of the bridge.Several of the piers had some Upto them and two were severelyrotated along with the Upping.These caused the adjacent spansto come off their piers and fall tothe ground. About a third of this

The first is the presence ofcolumn failures. resulting from alack of adherence to the

~prinCiple of designing a strong, column-weak beam system.

WATER AND WASTE WATERSYSTEMS

((A

pole-mounted and 5 ground-mounted transfonI1ers for power .Of these, five poles collapsedand one ground-mounted trans-fonI1er overturned. Commercialpower was intenI1ittent for twoto three weeks after theearthquake and 13 of 35 wellshad no power a month after theearthquake. One monthfollowing the earthquake, 35percent of Baguio was stillwithout water supply.

A second frequently occurringsituation is the installation of in-fill. typically 4" thick concreteblock walls. in the spacebetween the beams and thecolumns. Often there is a breakin the wall for a row of windows.Several resultant short columnfailures were observed. At theselocations there were no closelyspaced column rebar ties andconsequently very little ductilityso that a column rapidly lost itsstiffness and the load was thenpassed to the remaining columnlines. From a brief review of thebuilding plans in City Hall therehas been sQme detailing of close-ly spaced ties at these loCations.although in practice we did notobserve the installation of closelyspaced ties. such as 4" on cen-

I (. ter. as called for on some of the\'\Wbuilding plans. These columns

were severely overloaded be-cause of the earlier failure of thecolumns adjacent to the in-fillwalls; consequently a collapsemechanism tended to form.

Nearly all water supply in theimpacted area is from groundwater. The Local Water UtilitiesMministration, LWUA. hasresponsibility for water supplythroughout the Philippinesoutside Manila. A typhoon hitnorthem Luzon immediatelyfollowing the earthquake so thatrain runoff made pipeline leakdetection difficult. In Baguio,which was totally without pipedwater for four days, the rain alsoallowed residents to collectdrinking water .

BAGUIO WATER

The Kilometer Eight TreatmentPlant concrete bafl1e walls. withminimal reinforcing in the sedi-mentation basins. collapsed. Apreliminary estimate of pipelinedamage indicates 200 pipelinefailures occurred in the systemof 80 kIn of pipe. Because of theextensive permanent grounddefonnation from lateral spreadand slides. better perfonnance ofone type of pipe over anotherwas not identified.

Pump motor burn out was attri-buted to voltage fluctuation andsanding. A total of 8 of 35submersible pump/motorsrequired replacement during themonth following the earthquake.Baguio's 35 wells depend on 30

A third issue is that thecolumns' rebar ties were notadequately hooked. Often a 90degree hook was constructedrather than a larger bend that isrequired by the code to confinethe column steel. Consequentlythere is further reduction ofductility development and re-silience in these column hinges.In several failed columns bun-dled rebar was also observed.

It was reported that several ofthe severely damaged or col-lapsed buildings had been dam-aged during a previous earth-quake in 1985. Effective repairs

(:(II had not been completed beforethe subject earthquake. addingto the structural vulnerability .

Rebar detail1n Baguio.

5

was a major problem followingthe earthquake.

problem in restoration of watersystems is the lack of funds toget materials and make con-tracts. The disruption of service ehas also reduced revenues.

BAGUIO CrrY

In other regions the loss ofpower dIsrupted many watersystems. Dagupan was withoutany power for one day. followingwhich it was restored on arotation basis. The DagupanWater DIstrict had two emer-gency generators. Wells wereheavily damaged in all threegeographic areas. probably to agreater extent than what hasbeen documented in any pre-vious earthquake. Well casingswere offset from lateral spread inDagupan (5 of 17 wells) andAgoo ( 1 of 2 wells) making theminoperable. In Agoo. the oneremaining well's capacity wasreduced by one half.

Damage to roads and bridgeslimited access to the northwes-tem part of the Island of Luzonto a single bridge, creatingsevere traffic problems. Manybridges had soil behind theabutments settle creating a largestep in the roadway. Lateralspreading associated with lique-faction caused abutments tomove towards the center ofrivers. This cause lateral loadson piers and many piers lostfoundations due to liquefactionallowing them to tilt and dropthe spans that they weresupporting.

Baguio City .with a populationover 200.000. is located in amountainous region about 30miles from the causal fault andwas the most severely impactedcity. All three roads into the citywere closed for four days due tolandslides. A month after theearthquake only one road hadbeen reopened and several sec-tions were reduced to single lanetraffic. While damage to powerand communications systemswas not severe. the difficulty ingetting replacement partsresulted in the loss of power forseveral days and the loss ofcommunications for four days.

The water supply in the 1mpac-ted areas is primarily groundwater. There was widespreaddamage to wells due to defonna-tions caused by liquefaction.sanding of wells. and damage topumps due to fluctuations involtage in commercial power. InBaguio. one month after theearthquake only 22 of 35 wellswere operational. Unavailabilityof power is the major cause fordisruption. Large areas of lique-faction and subsidence causedextensive damage to the waterdistribution system. A major

Several modern engineeredstructures. designed to the UBCbuilding code. collapsed inBaguio. Factors that may havecontributed to some of these .failures were foundation damage 1due to liquefaction or subsi-dence. the use of concrete blockfiller walls topped by a row ofwindows creating a short -column effect. inadequately-spaced and sized ties confiningcolumns. the presence of strongbeam and weak columns, anddetailing of rebar .

~)

Concrete elevated tanks, foundin most systems on the plain,cracked and in Pozzorubio offset10 cm at the base. The concreteelevated tank design is similar toa standpipe with the tankbottom located three-quartersup from the base. The newconcrete elevated tank inCabanatuan was undamaged.At least three steel elevatedtanks collapsed. Many elevatedsteel tanks performed well, evenin Baguio where ground motionappeared to be the highest.Concrete tanks at grade werenot damaged except forconnecting piping. There wereno steel standpipes identified inthe impacted area.

~i

~

Pipeline damage resulted pri-marlly from liquefaction andlateral spread in the plain andcoastal areas. and from land-slide in Baguio. In Dagupan, 12out of 30 kIn of pipe must be re-placed because of the extensiveliquefaction-induced displace-ment. Central water distributionpoints were set up in areaswithout water. In Agoo. 17 pipefailures occurred in their two-month-old 1.5-kIn long system.Many of the failures in Agoowere from compression resultingin splitting the PVC pipe bells.

~ "

~~~~

.)

Dugapan liquefaction.Acquisition of repair materials

6

If

(()

now inverted and adjacent to thetower on the ground. havingbeen knocked off during theearthquake and crushing a carparked next to the tower. Theold control tower. a woodenframe structure. was notseverely damaged and was putback into seIVice. The airportplayed an important role in theemergency response after theearthquake as It was the onlyway to get into the area.

In Dagupan. a coastal city. therewas extensive liquefaction in anarea about four blocks by sixblocks. Three and four-stoIYstructures settled as much astwo meters. Many of thesebuildings settled uniformly sothat the ground floor wasexcavated and the buildingswere reoccupied.

SAN FERNANDO AREA

The Port of San Femando islocated approximately 270 kInnorth of Manila and Is the onlycommercIal port on the north-west coast of Luzon. This portconsists of eight warehouses andfive pIers that handle bulk drygoods and petroleum products.All facilItles sustained somedamage. As of July 20. replace-ment/repair costs were estima-ted at 3.3 mU1Ion U.S. dollars(24 PhilIppine Pesos / 1 U .S.Dollar) .

Spreading and tilting at Baguio airport.:(1,-

BAGUIO AIRPORr seriously affected by the earth-quake although small cracks(about 2 inches) and shifting didoccur at some constructionjoints. The concrete runway isabout 8" to 10" thick withsmooth and deforn1ed number 8rebar at construction joints. Theeast 3800 feet of the runwaycould be used and us militarycrews were flown in on the dayfollowing the earthquake to ef-fect repairs. With these repairs.the usable length of the runwaywas extended to 4800 feet.

Government Pier No. 1 has aconcrete deck supported by con-crete piles. A 2 foot gap openedin the concrete deck near theentrance to the pier and rebar inthe deck fractured at this loca-tion. There was extensive crack-ing at many other locations onthe deck and in the concreteapproach to the pier. At the pile-deck interfaces extensive crack-ing at the tops of the pilesexposed the rebar. Damage tothe piles was more extensive onthe sea side of the 2 foot crackin the deck. PIles in this areahad their cross-sectional area

The airport was the only physi-cal11nk for the community to therest of the country for four daysuntil one of the three roads con -necting it to other communitieswas put back into seIVice. TheBaguio Airport has a single1680 m-long concrete runwaywhich was carved out of the verymountainous terrain thatcharacterized the Baguio region.There are three tenIlinal build-ings, fire station, and old andnew control towers. The airportnormally operates only duringdaylight hours as the runway isunlit.

The most easterly airportstructure. located just adjacentto a slope of a stream runningbehind the structure. settledunifonnly across the structureabout a foot and a half relativeto the adjacent structures.which also appeared to havesettled slightly .

The earthquake caused severecracking across the runway.about 1200 feet from its westend. with blocks separating and

~ shifting so that there werecracks and vertical offset aslarge as a foot. The remaining3800 feet of the runway east ofthe cracked section was not

( l~

The pew airport control towerlost the windows and a heavyconcrete roof slab. The slab is

7

eralleaks at pipe flanges. whichwere stopped by tightening theflange bolts. All tanks were flat ~,bottom. unanchored and set on Ia prepared site with no ringfoundation or concrete mat.Many of the tanks settled with amaximum settlement from 8" to12". None of the tanks hadelephant foot type buckling.Two tanks appeared to be slight-ly buckled due to differentialsettlement. although the originalstate of the tank is not known.

One of the most striking impactsof the earthquake at the CALTEXsite was the extensive lateralspreading and subsidence thatoccurred. Defonnation in onepipe run indicated that thelateral spread across the sitewas 33". There were many indi-cations of lateral spreading andsubsidence throughout the site.Several of the tanks were tiltedand the maxirnum differentialsettlement observed across thebase was 6".

San Fernando: pre-earthquake corrosion.

reduced almost in half at thepile-deck interface. However .extensive corrosion in theexposed rebar indicates thatmuch of this damage occurredsome time prior to the July 16earthquake. Damage reportsfrom the port stated that thepiles deflected an average ofabout 3 ft. towards the sea.

connect them to the piers at theport. The pipelines are 6"schedule 40 pipe and are buriedin sand 2 to 3 feet deep. Theywere no breaks in the pipelinebut there were numerous leaksat flanges. The first shipment ofpetroleum products to come intothe port was about 3 weeks afterthe earthquake.

.,!~DAGUPAN

In the Dagupan ar~a several gasstations were obseIVed with theirlarge gas storage tanks risen tothe surface. These tanksfloated up when the soil in

Two tank fanns were visited witha total of 14 storage tanks and amaximum capacity of 53,000bbls. There were no pipe breakson the sites but there were sev-

The coal pier also displacedtowards the sea causing theconcrete deck approach tocollapse, gaps to open in whatappeared to be constructionjoints in the deck, piping to leak.and minor damage to the coalconveyor. Similar damage wasnoted in the report concerningthe PHILEX pier.

~

Cracks. averaging about 2inches. were observed aboutevery 60 feet in the concrete dikefacing the harbor betweenGovernment Pier No. 1 and thecoal pier. They appeared to bedue to lateral spreading betweenthe two piers.

Several oil companies had tankfarms near the port that seIVe asa dIstribution center for oilproducts for the northeasternpart of the island of Luzon. Thetank farms are served by twopipelines. about a mile long. that

e!

Road delays.

8

employer in the city. The smal-ler plant manufactures electron-ic controllers for aircrafthydraulic actuators.,

which they were buried liquefied.Concrete slabs covering thetanks buckled up as much as

.At the time of thevisit. the tanks had beenremoved from the ground andthe holes from which they wereremoved had been filled.1Gas stations in Dagupan werealso getting their productstrucked in from Manila ratherthan from San Fernando.

,~

spalling and cracking in col-umns and adjacent in-fill wallsat the building comers. Theother structure was essentiallyundamaged. The difference inbuilding perfonnance may relateto the damaged building's loca-lion toward the downhill side ofthe site. apparently on filled soil.The damaged building sufferedwholesale collapse of suspendedceiling fixtures. compared tominor effects in the undamagedbuilding.

EFFECTS ON INDUS1RYEquipment inside the buildingsslid several inches. and in a fewinstances overturned. However .because most attachments toequipment had adequate slackto accommodate small displace-ments. damage was generallyminimal. It appeared that thefacility could return to normaloperation within about twoweeks of the earthquake.

The economy of central Luzon,where the earthquake affectswere greatest. is based primarilyon agriculture. The area heavilyshaken by the July 16 earth-quake contains only a fewregions of heavy industry.

The integrated circuits plantincludes several one- and two-story concrete frame buildingswhich had minor structuraldamage. Most structural dam-age was caused by settlement offilled soil along the periphery ofthe buildings. Soil failure frac-tured buried piping. includingfIre water mains serving thebuildings. Inside the buildings,unanchored equipment slid asmuch as 1/2 meter. tearingattached conduit. piping. andducts. FJxtures suspended fromceilings. such as rod-hung pi-ping. ducts. diffusers. lightfixtures. and T -bar supportedceiling panels. fell throughoutthe complex. It appeared that 2-3 weeks would be requiredbefore normal operations couldbe resumed. In general. adverse earthquake

effects to industry consistedprirnarily of damage to buildingstructures. including severaltragic collapses. Less severeeffects leading to business inter-ruption included equipment slid-ing. and falling ceiling-mountedfixtures. resulting in someinstances in fractured utilityconnections such as piping.Perhaps the greatest long termeffect on industry will not bedirect damage. but indirect ef-fects due to closure of highwaysthroughout central Luzon. fromlandslides and bridge failures. Itappears that the normal roadtransport system for raw materi-als. products. and personnel.would be disrupted for months.

The hydraulic controllers plantexperienced similar problems.although to a milder degree. Theplant includes two one-stoIYconcrete frame buildings withmasonry in-fill walls. Onestructure suffered severe

The most heavily damaged areanear the city of Baguio happensto be one of the few centers ofindustry as well as tourism. The

!(I) mountains surrounding Baguio" ' include several large mining

operations. some of whichreported structural damage fromthe earthquake. In the daysimmediately following theearthquake. the mines were notaccessible due to landslidesblocking the roads.

Most industrial operations nearBaguio are located in the ExportProcessing Zone (EPZ) , near thecity airport. The EPZ includeswarehouses and light manufac-turing operations, housed inlow-rise concrete frame build-ings. Within the EPZ, a total offive concrete frame buildingscollapsed, reportedly trappingseveral hundred workers in theruins. One collapsed building, astorehouse for plastic resin,caught fire the day following theearthquake.

CASUAL11ES

The earthquake claimed over1,600 lives. Building and soilfailure accounted for mostfatalities and serious injuries.Fatalities and serious injurieswere concentrated in areas ofheaviest structural damage andlandslides. For example, in

gThe EPZ includes two large man-ufacturing operations for elec-tronic components. The largerplant manufactures integratedcircuits, and is the largest single Road bed failure.

~

Luzon College.

training and equipment ham-pered local rescuers. Philippineand U.S. military personnel(from Subic Bay and ClarkAFB)later arrived in Cabanatuan withheavy equipment.

Baguio City. where dozens ofmulti-stoIY engineered struc-tures were severely damaged.hospitals and funeral parlorsreceived 959 cases (612 injuredsurvivors and 347 deaths) byJuly 21. Hundreds more werelisted as missing insidecollapsed buildings. Multi-stoIYhotel, school. office. and factoIYbuildings were the sites of majorcasualties. In Baguio City(approximately 200.000 popula-tion) twenty-sevefl modern. engi-neered, reinforced concretestructures experienced total orpartial collapse. Other fatalitiesoccurred at low-rise structures.such as schools, when unrein-forced masonry infill wallscollapsed. Conversely, less thanforty fatalities, but hundreds ofminor injuries, were confirmedin Pagasinan Province in spite ofserious liquefaction damage tohundreds of structures.

The Philippine earthquakeunderscores the need to examinethe utllityand role (other thansymbolic) of foreign rescueteams. Typical of past earth-quakes. foreign search andrescue specialists includingteams from the U.S.. England.and Japan arrived too late tomake a difference. For example.the U.S. DARrTeam rescuedone survivor at the cost of$400.000. In this earthquake.the foreign teams also broke offand left too soon. Local minersrescued survivors from thecollapsed Hyatt Hotel ahnost twoweeks after the earthquakes andlong after the US and otherteams had given up and pulledout. Clearly .future foreignassistance should be directed atimproving local search andrescue capabilities.

No hospitals collapsed. The 100bed Dona Gregoria MemorialHospital in La Union Provincewas the only provincial hospitalsuffering significant structuraldamage and may requirereplacement. Several 10 and 25bed facilities also had somelocalized structural damage.Only one major Manila hospitalsuffered localized structuraldamage forcing the transfer ofsome patients.

Landslides buried villages andclustered hillside houses andswept cars and buses off heavilytraveled roads into ravines,causing many casualties in themountainous Benguet andNueva Vizcaya Provinces.Fatalities and injuries fromthese areas, when tallied, willgreatly increase the officialcasualty totals.

Several large hospitals in Baguioand smaller facilities elsewhereevacuated patients and staff andremained operating on lawnsand in parking lots even afterthey were certified as safe bystructural engineers.

Casualties were extremely lightin Manila.

Extensive damage to oxygentanks. which are mobile andunrestrained. in Philippinefacilities. prompted emergencyrequests for gauges to replacethose broken when the cylinderstoppled.

SEARCH AND RESCUE

1111

II

Baguio, Cabanatuan, and Agoowere the major sites oforga-nized search and rescue activi-ties. Predictably, the bulk ofrescues were made by fellowbuilding occupants and localrescue personnel. In Baguio,local gold and copper miners,and Philippine Military Academycadets arrived quickly to shoreup and search collapsed build-ings. In Cabanatuan, staff, stu-dents, and parents made most ofthe rescues in a collapsed six-story school building. Lack of

WJ

HEALTH CARE SYSTEMRESPONSE

The emergency medical responsewas hampered by lack ofcommunications in the first fivedays. and impaired accessibilityto the striken areas. Helicoptersand light planes were able to de-liver some supplies immediatelyto Baguio. However. runwayand control tower damage mini-mized use by larger aircraft forfour days. Bridge and road fail-ures severed vital arteries in the

The earthquake left the Philip-pine health care system largelyintact. However. the perceptionof damage among hospital staffmembers and the fear of subse-quent aftershock damage causedsignificant service disruption.

. ~!

'~ljJc Ij

10

~, ic

l~

low-lying areas as well hamper-ing emergency response andrelief efforts. Fortunately for

~BaguIo. the staffs of four major3 hospItals were available to

respond to the emergency .Thecity also served as a regIonalmedIcal supply depot so drugsand medications were abundant.Major hospItals in Manilasuffered little structural damageand served as a transfer pointfor the seriously Injured. As ofJuly 23. 44 patients had beenair-lifted by helIcopter from thedamaged area (36 from BaguIo). Cojuangco Bridge approaches.

LONG TERM IMPACTS JAPANESE INVESTIGATIONThe injury situation in themountains to the northeast ofBaguio is more ominous. Tendays after the earthquake. therestill had not been a good assess-ment of damage and casualtiesin these rural areas cut off bylandslides.

On August 4 a group of 14Japanese researchers fromuniversities and constructioncompanies (6 from universitiesand 8 from companies: 10 struc-tural engineers. 2 geotechnicalengineers. and 2 civil engineers)left Narita.

Dagupan City (population120,000) lost about 55% of itscentral business district whenthis area sunk three meters dueto liquefaction. Plans for relo-cating much of the affected areaare under discussion. BaguioCity , a vacation center, lostmany of its largest hotels. Whileone road into Baguio was openintermittently, the other threearteries are closed for a mini-mum of four to six months.Reconstruction in the higherelevations will be further ham-pered as earthquake and rainweakened slopes continue to fail.Depression, post -traumaticstress disorder, and otheremotional problems will bepervasive long-term healthimpacts during the recoveryperiod.

Iuespectlve of damage to theirhomes, many, fearing after-a\,\ShOCks, chose to set up tempora-

:\ IJxy shelters outside or in nearbyparks. Persistent rains, andinterrupted water and sewageservice made life in these tentcities miserable and createddismal sanitary conditions forthousands of homeless families.Despite the potential for seriousepidemics, rumors to this effect,and widespread public concern,health authorities respondedsuccessfully and no maj oroutbreaks were verified.

On August 6. they investigateddamage in Baguio in fourgroups. At City Hall. the struc-tural drawings of 9 damaged(collapsed) buildings were seen.The drawings of the Hyatt Towerwere missing. but the structuraldrawings of the Hyatt Terraceswere present. There was nottime to study the drawings andcalculations in detail. but thebase shear coefficients weregenerally between 0.05 to 0.10.The building code was adaptedfrom the UBC. The structuralfactor K was 0.67. There wereno calculations with structuralwalls. In the drawings of onehotel. beam bottom reinforce-ment was anchored for gravityloading conditions (straightanchorages in external beam-column jOints) .The spacing ofstirrups and ties was nonnallyat 100 mm o.c. at the memberends (approximately 3/4 of themember depth) and wasincreased to 200 mm to 250 mmo.c. toward the center. Thelateral reinforcement in the

0'

li

1'f

~

IU

Repair work.

~

11

beam-column jOint was specifiedminimal (one to two ties). Theconcrete strength was normally3,000 psi, and the steel strengthvaried from 40,000 to 50,000psi. In most cases, span lengthswere 4.5 to 6.0 m, and morethan 12 m if prestressing wereused.

LA TRINIDAD

"A building under constructionon the Benguet State Universitycampus was severely damagedespecially in the beam-columnjoints. and in the soft first storymechanism. The Justice Hall inBauang appeared severelydamaged from the outside. but acareful inspection revealed thatthe damage was mainly concen-trated in non-structural parti-tions and windows. Very littledamage occurred in structuralmembers.

The typical failure modes in thisearthquake were

( I) failure in bearn-colurnn jointscaused by no or little lateralreinforcement in the joint (bothinterior and exterior) .

(2) shear failure of columns attheir mid-height caused by widespacing (tyPically 6 rnrn bars at300 mm o.c.) of shearreinforcement with 90 degreebends at the ,ends.

tory at the bottom of the secondstory because no reinforcedconcrete girder existed at theroof level (timber trusses wereconstructed in the transversedirection to support the roofwith small connections at thetop of the second storycolumns); and the library build-ing with shear failure of columnsshortened by non-structuralblock walls. The Agoo BuildingCenter building (3 stories) andits storage facility collapsed.The Agoo Public Market building(two stories, seven spans in thelongitudinal direction and fourspans in the transverse direc-tion) failed in the first story sidesway mechanism. The buildinghad two structural reinforcedconcrete walls at every span, butfailed in the longitudinaldirection caused by shear failurein the first-story columns.

(3) the interaction of non-structural walls (of slightlyreinforced hollow blocks) withreinforced concrete columns.making short columns.

DIGDIG

Faulting was observed at Digdig . ,'i(north of Cabanatuan and San "

Jose). One offset at Digdig was3.5 m horizontal movementmarked on the paved highway.According to a seismologist fromKyoto University .a fault offset ofthis sIze is not often seen on theground surface. and he wishedto buy the land to preserve theevidence !!

In the city of Dagupan manybuildings tilted and sank fromliquefaction. Very littlestructural damage was observedexcept for collision of the tiltingbuildings. The roads in the townwere covered with fme greenishsands. In one building. theground floor was lifted almost 50cm at the mid-span when thebuilding sank. The base of theexterior first story columnsmoved because there were no tiebeams.

AGOO(4) shear failure at the columnbase because columnreinforcement was spliced at thebottom of the column. Buildings in Don Mariano

Marcos Memorial Universitywere severely damaged: onestadium under construction inbeam-columnjoints; one dom1i-

The structural walls should havebeen utilized to reduce thestructural deformation.

~~

There were many undamagedengineered buildings: Le., theperformance of Mt. Crest Hotel(a prestressed precast concretebuilding) was superb. Theresident engineer of the hotelhad a set of structural drawingswhich showed a few cases inwhich the beam reinforcementwas anchored outside of thecolumn cage.

~~

A geotechnical group visited Sto.Thomas (the whole village sankduring the earthquake) andDagupan (one third of the townwas liquefied. causingsettlement and tilting ofbuildings) . Dugapan l1quefactiOn.

12