EARTHQUAKE DAMAGE TO BRIDGES 31

Transcription

1 BEHAVIOUR OF BUILDING, BRIDGES, DAMS AND PORTS DURING BHUJ EARTHQUAKE OF JANUARY 26, 2001 Pankaj Agarwal, S.K. Thakkar and R.N. Dubey Summary A massive earthquake of magnitude (M L = 6.9 on Richter scale, m b =7.0, M S = 7.6 and M W = 7.7) occurred near Bhachau, Gujrarat on the morning of 51 st Republic day of India (January 26, 2001, Friday) at 08:46:42.9 hours (IST). A number of infrastructures facilities such as building, bridges, dams and ports were damaged. A summary of damages and lesson learnt that occurred due to this earthquake are reported here. DAMAGE IN REINFORCED CONCRETE BUILDINGS Reinforced concrete buildings have been damaged on a very large scale in Bhuj earthquake of January 26, The principal causes of damage to buildings are due to presence of soft storeys, floating columns, mass irregularities, poor quality of material and faulty construction practices, inconsistent seismic performance, soil and foundation effect, pounding of adjacent structures and inadequate ductile detailing in structural components were features of damages. Figure 1 shows some of the examples of failure in RC buildings. (a) Soft storey failures in Apollo Apartment at Ahmedabad, ground floor was completely collapsed (b) Nilima Park Apartment, Ahmedabad, large scale damage in the upper floors due to floating columns construction (c) Collapse of half portion of A-block of Mansi Complex, Ahmedabad due to presence of a massive swimming pool on roof (d) Anand building, Bhuj, damage resulting from pounding Figure 1: Typical example of failure in Multi-storied RC building in Bhuj earthquake, 2001 EARTHQUAKE DAMAGE TO BRIDGES 31

2 The bridges both on the highway and railway have suffered damages due to Bhuj earthquake. Old Surajbari bridge more than 30 year old, 2 lane highway bridge near Bhuj that sustained significant damage. A New Surajbari two lane highway bridge close to the existing bridge was under construction also suffered damage to its elastomeric bearings and upstands. The Machhu bridge consisting of three spans of 27.6 m also suffered damage. It is a balanced cantilever bridge resting on low height piers. The approach to the bridge has developed cracks. The seven span Railway bridge at Bhachau sustained minor damage. It was a steel girder bridge having simply supported spans resting on about 4m high RC piers. The damage to bridge piers and its approaches were repaired and bridge was being used after the earthquake. Road bridge at Bhachau, is a multi-span simply supported bridge on low height piers under construction. The bridge pier cap got cracked with wide separation from the bearing blocks and tilting of pier in the end span. The damage also occurred to abutment and approaches. Figure 2 shows some typical example of damages in bridges in Bhuj earthquake, 2001 (a) Old Surajbari bridge (damage to bearings, approaches, pounding of superstructure) (b) Railway bridge near Bhachau, minor damage to bridge piers and approaches (c) Multi-span Road bridge on low height pier near Bhachau, bridge under construction (cracking of piers, separation from bearing blocks) (d) Multi-span Road bridge on low height pier near Bhachau under construction (severe damage to approach) 32

3 (e) Rudramata bridge is functional without any repair (f) Rudramata bridge, Bhuj (cracking of road and settlement of approach road) Figure 2: Typical example of damages in highway and railway bridges in Bhuj earthquake, 2001 EARTHQUAKE DAMAGE TO DAMS There is an evidence of extensive damage to medium and minor irrigation schemes in Kachchh and Saurashtra regions of Gujarat. There are 20 medium and 165 minor irrigation schemes in the kachchh district. Out of these 5 medium and 14 minor irrigation schemes are severely damaged and 11 medium and 125 minor irrigation schemes are moderate to heavily damaged. In Saurashtra region, there are 2 major, 11 medium and 287 minor irrigation dams. Out of these reportedly 9 medium dams are severely damaged and 31 are moderate to heavily damaged. Majority of damages are in the form of cracking of earthen dams. The width of cracks vary from few cm to 50/60cm. Similarly the depth of these cracks varies upto 8m or more. Earth dams such as Rudramata, Kasawati, Fatehgarh, Suvi, Tappar, Kaila, Chery and Shivalakha are damaged severely. The damage to the earth dams includes longitudinal and transverse cracks, settlement and displacements. Figure 3 shows some typical example of damages in earthen dams in Bhuj earthquake, 2001 (a) Rudramata Irrigation Scheme: River Khari, village - Nokharia (b) Head regulator badly damaged, Rudramata Irrigation Scheme (c ) A wide crack (4 to 5 inches) on crest of Kayala dam along the length (d) Head regulator damaged, Kayala dam 33

4 (e) U/s slope failure- cracks along the length of Niaona dam (f) Head regulator and u/s slope failure of Nirona dam Figure 3: Typical example of damages in Earthan dams in Bhuj earthquake, 2001 EARTHQUAKE DAMAGE TO KANDLA PORT The Kandla Port is located approximately 40 km to the South of epicenter of earthquake. The R.C. Jetties, Wharf structures, Ware Houses, Oil tankers, Navigation tower, Administrative building suffered damage in the earthquake. The cracking of filled ground is observed at many places. There is wide spread liquefaction in the area. The ground in the area suffered damage in the form of wide spread cracking and settlement. The older jetties supported on 0.5 m diameter piles are damaged at same places. The new jetties supported on 1.0 m diameter piles performed well. The navigation tower, 22 m high six storeyed R.C. frame navigation tower got tilted. The building is supported on pile foundations. The tilting of tower is possibly due to lateral ground deformation and liquefaction of soil. The administrative building adjoining the navigation tower had a soft storey failure. Many of the R C Piles of 50 year old jetty are found to be cracked 30 cm below the pile caps. Lateral spreading of the soil led to the lateral translation of piles. Both flexural and shear cracking were observed in piles. (a) Tilting of navigation tower towards water fronts (b) Soft-storey failure to administrative buildings of Kandala Port Figure 4: Typical example of damages in Kandala Port in Bhuj earthquake,

5 LESSONS LEARNT FROM DAMAGES The occurrence of Bhuj earthquake, 2001 has caused significant damage to infrastructures facilities. The lessons learnt from damages are presented below: i. The multi-storeyed reinforced concrete buildings with vertical irregularities like soft storey construction and buildings with mass irregularities such as massive swimming pool on the roof of the building and building with floating columns should be designed on the basis of dynamic analysis and inelastic design. The ductility provisions are most important in such situations. ii. The types of damage that occurred in bridges are categorised as follows: damage to bearings and stoppers, pounding action of adjoining spans, cracking and tilting of piers, damage to abutments and retaining walls, damage to bridge railing and parapets, cracks in approach road, cracking on road near expansion joints, cracking of river bed and liquefaction of soil. The damage to the earth dams mainly due to longitudinal and transverse cracks, settlement and displacements. 35