Analysis On Near-field Earthquake Response Of Reinforced Concrete Plane Frame Structure

Earthquake is one of the most serious natural disasters known to mankind.Earthquake is accompanied by huge energy release,which brings severe life threatening and huge economic losses to mankind.The near field earthquake zone is closer to the seismic fault zone,and the seismic energy can reach the site in a short time.The structural response caused by the ground motion is very significant.The existing research results mainly focus on the comparison of near field and far field earthquake responses for different structures.Therefore,the research work of structural response of near field earthquake velocity pulse has theoretical significance and engineering application value.The structure response of frame structure under the effect of near field velocity pulse earthquake has been studied,the following research work is carried out in this paper.Based on the fault distance of 0-20km,velocity pulse earthquake records in the near field are collected by using the US Pacific Earthquake Research Center PEER database.126 earthquake records with velocity pulses in the near field are collected totally by using the present PEER database.The list of the 126 earthquake records is given in order of the velocity peak values of horizontal records from big to small.The peak values of the 126 near-field velocity pulse earthquake records are mainly distributed among 30-150 cm/s.From the point of view of the number of earthquake records,the records of Chi-Chi earthquake,which includes 29 records,are the most.From the earthquake event point of view,the 126 earthquake records come from 29 earthquake events.The relationships between peak values of velocity pulses,PGV/PGA values and site classification,moment magnitude,fault distance,are studied respectively.From the site classification point of view,there are more earthquake records on the C and D sites.The earthquake records with peak values of velocity pulses bigger than 100cm/s are mainly on the C and D site,totally in the earthquake records with moment magnitude above 6.5,and totally distributed within the fault range of 0-10 km.The earthquake records of PGV/PGA values bigger than 0.2 are mainly on the C and D site,almost in the earthquake records with moment magnitude above 6.5,mainly distributed within the fault range of 0-10 km.The PGV/PGA values in earthquake records with moment magnitude above 7.5 are almost bigger than 0.2,even bigger than 0.5.The structural response of a two span five floors reinforced concrete plane frame structure under the action of velocity pulse and no velocity pulse earthquake waves have been studied.Four groups earthquake records with horizontal single direction velocity pulse were selected 8 in all.which were two groups ground case I earthquake waves(RSN879,RSN1148)and two groups ground case II earthquake waves(RSN1530,RSN1182).For the two span five layer plane frame structure under earthquake waves action with velocity pulse and no velocity pulse respectively,the lateral displacement for the top of the first layer column relative to the base,top displacement and base shear of structure have been studied.The results show that,compared with no velocity pulse earthquake wave,under the action of pulse velocity earthquake,the lateral displacement for the top of the first layer column relative to the base,top displacement and base shear of structure were increased.Under the action of four groups velocity pulse earthquake waves,compared with no velocity pulse,average value of the lateral displacement for the top of the first layer column relative to the base increased by 177.6%,160.9%,24.7%and 26.7%respectively,the peak displacement were increased by 133.3%,134.4%,17.4%and 13.1%respectively,the base shear were increased by 106.2%,33.9%,19.2%and 7.3%respectively.The lateral displacement for the top of the first layer column relative to the base average value increased significantly.For the two span five floors plane frame structure,two groups ground case I site earthquake waves(RSN879 and RSN1148)were used to further calculate the bottom shear force values of each layer column,the moment envelope diagram of the first floor beam column,and the Mises stress diagram of the first floor concrete and reinforcement.The results show that the shear force of each column under the action of the near field velocity pulse earthquake waves increases in varying degrees.The moment envelope of the first layer beam column under velocity pulse earthquake action is larger than that without velocity pulse earthquake,and the moment value of the first layer beam has increase of different degrees.The maximum value of hogging moment in the first layer beams appears on the right side of the short span beam under the action of the velocity pulse earthquake.In the Mises stress cloud map of the first layer under the velocity pulse earthquake,the Mises stress value of the steel bar and concrete at the bottom of the column are concentrated.The longitudinal bar at the bottom of the column are easy to yield.