precast concrete construction - IFET College of Engineering

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are commonly used for floor and roofstructures in this type of construction.Slab-Column Systems with Shear WallsThese systems rely on shear walls to sustainlateral load effects, whereas the slab-columnstructure resists mainly gravity loads. Thereare two main systems in this category:• Lift-slab system with walls• Prestressed slab-column systemLift-slab systems were introduced inthe last decade of the Soviet Union (period1980-1989) in some of the Soviet Republics,including Kyrgyzstan, Tadjikistan, and theCaucasian region of Russia, etc. This type ofprecast construction is known as “SeriaKUB.” The load-bearing structure consistsof precast reinforced concrete columns andslabs, as shown in Figure 10. Precastcolumns are usually two stories high. Allprecast structural elements are assembled bymeans of special joints. Reinforced concreteslabs are poured on the ground in forms, oneon top of the other, as shown in Figure 11.Precast concrete floor slabs are lifted fromthe ground up to the final height by liftingcranes. The slab panels are lifted to the topof the column and then moved downwardsto the final position. Temporary supports areused to keep the slabs in the position untilthe connection with the columns has beenachieved. In the connections, the steel bars(dowels) that project from the edges of theslabs are welded to the dowels of theadjacent components and transversereinforcement bars are installed in place.The connections are then filled withconcrete that is poured at the site.Most buildings of this type havesome kind of lateral load-resisting elements,mainly consisting of cast-in-place or precastshear walls, etc. In case lateral load-resistingelements (shear walls, etc.) are not present,the lateral load path depends on the abilityof the slab-column connections to transferbending moments. When the connectionshave been poorly constructed, this is notpossible, and the lateral load path may beincomplete. However, properly constructedslab-column joints are capable oftransferring moments as shown by severalfull-scale vibration tests performed inKyrgyzstan on buildings of this type.Another type of precast system is a slabcolumnsystem that uses horizontalprestressing in two orthogonal directions toachieve continuity. The precast concretecolumn elements are 1 to 3 stories high. Thereinforced concrete floor slabs fit the clearspan between columns. After erecting theslabs and columns of a story, the columnsand floor slabs are prestressed by means ofprestressing tendons that pass through ductsin the columns at the floor level and alongthe gaps left between adjacent slabs (seeFigure 12). After prestressing, the gapsbetween the slabs are filled with in situconcrete and the tendons then becomebonded with the spans. Seismic loads areresisted mainly by the shear walls (precastor cast-in-place) positioned between thecolumns at appropriate locations. Thistechnology has been used in Yugoslaviaduring the last 40 years under theproprietary name, “IMS Building System,”and it can be found in all major Yugoslavcities, including such as Cuba, the
Philippines, and Egypt. A typical buildingunder construction.EARTHQUAKE PERFORMANCEThere is a general concern among theearthquake engineering communityregarding the seismic performance ofprecast construction. Based on experience inpast earthquakes in Eastern European and inCentral Asian countries where these systemshave been widely used, it can be concludedthat their seismic performance has beenfairly satisfactory. However, when it comesto earthquake performance, the fact isthat “bad news” is more widely publicizedthan “good news.” For example, the poorperformance of precast frame systems ofSeria 111 in the 1988 Spitak (Armenia)(M7.5) earthquake is well known (seeFigure 14). However, few engineers areaware of the good seismic performance (nodamage) of several large-panel buildingsunder construction at the same site, asshown in Figure 15; these large-panelbuildings were of a similar seria as the largepanelbuildings described in the WHEReport 55 from the Russian Federation(Seria 464). The buildings of Seria 111 weresimilar to the precast concrete frame systemof Seria IIS, described in the WHE report 66(Uzbekistan). The precast prestressed slabcolumnsystem (IMS Building System)described in WHE Report 68 (Serbia andMontenegro) has undergone extensivelaboratory testing that predicted excellentresistance under simulated seismic loading.These building have been subjected toseveral moderate earthquakes withoutexperiencing significant damage. Due totheir large wall density and box-likestructure, large-panel buildings are very stiffand are characterized with a rather smallfundamental period. For example, a 9-storybuilding in Kazakhstan has a fundamentalperiod of 0.35 to 0.4 sec (WHE Report 32).In general, large-panel buildings performedvery well in the past earthquakes in theformer Soviet Union, including the 1988Armenia earthquake and the1976 Gazlyearthquakes (Uzbekistan). It should benoted, however, that large-panel buildings inthe area affected by the 1976 Gazlyearthquakes were not designed with seismicprovisions. Most such buildings performedwell in the first earthquake (M 7.0), butmore damage was observed in the secondearthquake that occurred the same year (M7.3), as some buildings had been alreadyweakened by the first earthquake (RussianFederation, WHE Report 55). Large-panelbuildings performed well in the 1977Vrancea (Romania) earthquake (M 7.2)and in subsequent earthquakes in 1986 and1990 (Romania, WHE Report 83).SEISMIC-STRENGTHENINGTECHNOLOGIESAccording to WHE reports, no majorefforts have been reported regarding seismicstrengthening of precast concrete buildings.However, seismic strengthening of precastframe buildings was done in Uzbekistan(WHE Report 66). The techniques usedincludethe installation of steel straps at the columnlocations (see Figure 16) and reinforcing thejoints with steel plates to provide additionallateral confinement of the columns.Conclusion:
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precast concrete construction - IFET College of Engineering

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