Major Parameters Affect the Non-Liner Response of Structure Under Near-Fault Earthquakes

Near-fault ground motion can be identified by the presence of a predominant long duration pulse in the velocity traces mainly due to directivity effect. This pulse exposes the structure to high input energy at the beginning of the earthquake which leads to a higher response in comparison with the ordinary ground motions. This paper investigates 79 earthquake records with different properties to achieve three goals: the first aim is to compare between the linear and nonlinear response of SDOF systems under near-fault and far-fault earthquakes. While the second objective is to examine the parameters that control the characteristics of near-fault earthquakes. Two factors have been studied which is PGV/PGA ratio and pulse period. Finally, the seismic code provisions related to the near-fault earthquakes were evaluated in term of the elastic acceleration response spectrum, the evaluation is adopted for American Society of Civil Engineers code ASCE 7 and Uniform Building Code UBC. The results lead to the following conclusions: with respect to a specific PGA, the near-fault earthquake imposed higher response in comparison with far-field earthquakes. The near-fault earthquakes become severe as the PGV/PGA and pulse period increase. The interested seismic codes can cover the actual behavior based on the average response of a certain amount of data, while it may become non-conservative relative to an individual record

Influence of near-fault characteristics on inelastic response of multi-storey building with intensity measurement analysis

Studija je izrađena kako bi se ostvarila tri cilja: (1) usporedba neelastičnih odziva građevina na bliske i udaljene pobude, (2) istraživanje utjecaja odnosa impulsnoga perioda i perioda konstrukcije te (3) ocjena niza mjerenja intenziteta (IM) za bliske potrese. Postojeća armiranobetonska zgrada s 35 katova analizira se u okviru prvoga i drugoga cilja, dok se u okviru trećega cilja analiziraju tri okvirne građevine s po 6, 13 i 20 katova. Rezultati pokazuju da kod bliske pobude može na građevinama doći do prekoračenja razine sposobnosti zaštite života. Osim toga, točnost mjerenja intenziteta u velikoj mjeri ovisi o periodu titranja građevine i o funkciji koja se rabi za izračunavanje vrijednosti IM.This study is presented to achieve three objectives: (1) to compare between the inelastic responses of buildings under near and far fault excitations, (2) to investigate the effect of the pulse to structural period ratio, and (3) to evaluate a set of intensity measurements (IMs) in terms of near fault (NF) earthquakes. A real reinforced concrete building with 35 storeys is analysed in the scope of the first and second objectives, whereas the third objective involves three general-frame buildings consisting of 6, 13, and 20 storeys. Results show that the NF excitation can drive the building to exceed its life safety performance level. Furthermore, the accuracy of the IM highly depends on the vibration period of the building and the function used to calculate the IM

Numerical analysis of RC wall with opening strengthened by CFRP subjected to eccentric loads

U radu je provedeno numeričko ispitivanje središnjeg otvora u ab zidovima s CFRP ojačanjem i bez njega podvrgnutim ekscentričnom vertikalnom opterećenju s linearnim prirastom. Šest zidnih ploča u mjerilu 1 : 2 modelirane su u računalnom programu ABAQUS u svrhu procjene učinka ojačanja. Analiza je pokazala da na nosivost zida u smislu maksimalnog opterećenja utječe debljina CFRP-a. Utvrđeno je da varijacija debljine CFRP-a ima značajan utjecaj na krajnju nosivost, pojavu pukotina, glavnu plastičnu deformaciju betona i ekvivalentno naprezanje.Numerical analysis of the central hole in RC walls with and without CFRP, subjected to uniform eccentric vertical line load, is presented in this paper. Six half-scale wall panels were modelled using the ABAQUS software to estimate the strengthening effects. The analysis revealed that the load capacity of the wall in terms of maximum load carrying capacity is influenced by CFRP thickness. It was found that the variation of CFRP thickness greatly influences the ultimate load carrying capacity, crack patterns, principal plastic strain of concrete, and equivalent stress

The Behavior of Concrete Cantilever Retaining Walls During Far-Field and Near-Fault Earthquakes

The dynamic behavior of retaining walls is a complicated subject and a considerable design challenge, particularly under seismic conditions. Seismologists and investigators have an interest in near-fault earthquakes with significant velocity pulses because it can cause considerable displacements in constructions with respect to far-field earthquakes and consequently rise the hazard of earthquake-caused failure of structures. Despite there are several studies have investigated the seismic behavior of retaining structures, but the researches about retaining walls subjected to the influence of near fault like pulse earthquakes is still not adequate. The current study targets to numerically assess the dynamic performance of concrete cantilever retaining walls during far field ground motions (FFGMs) and near-fault ground motions (NFGMs). The nonlinear analysis of time history is conducted using the finite element method for three cantilever retaining wall models. The results of the analysis gained in terms of top horizontal displacement of the wall, active seismic earth pressure, and acceleration response of the system, which have been considered to recognize the impact of near fault earthquake on retaining structures. Additionally, the influence of different PGA of NF and FF earthquakes has been studied

Sudden collapse of steel water tower tank due to compound openings in critical zone

AbstractDespite previous efforts to detect concentrated stresses in structures with holes, a complete understanding of structures that contain compound openings in addition to screw holes in critical stress areas is incomplete, especially for structures that are subject to sudden collapse. This study aims to conduct a laboratory test program to simulate a suddenly collapsed tank that contains compound holes in addition to the screw holes distributed on the cleaning opening located in the critical stress area. Six laboratory simulated models with two repeats for each are tested to represent the stages of implementation of the cleanout opening and to find out the causes of the sudden failure of the tank. Significant reduction in resistance when having a centre hole compared to the control plate. The importance of the stiffeners is evident in this region, as the resistance decreased slightly compared to the control plate by adding reinforcement plates on both sides. The resistance drop remains almost constant despite the stiffening panels being punctured on both sides with the same diameter as the main hole, which confirms the continued importance of the stiffeners at this stage. An improvement in resistance was observed when a cap was added to one of the holes in the stiffeners. A slight change in resistance was also observed when the cap was pierced with another hole to weld the cleaning pipe due to the failure remaining within the screw holes surrounding the main hole. In conclusion, the safety factor should be increased in areas that contain compound openings

Numerical Modal Analysis of Reinforced Concrete Slab with Opening

Openings in reinforced concrete (RC) slabs are usually created as a result of variations in construction function, architectural or mechanical necessities. Heavy equipment loads resulting from mechanical system of any building are often carried by RC slabs. Even the static analysis and design of RC slabs with opening is not clearly stated in the available international Codes, dynamic analytical solution for such structure is complex. In this paper, numerical analysis based on finite element approach is utilized to implement the modal analysis of RC slabs. Opening size and position was parametrically studied. Slab natural frequency or periods in addition to, the mode shape were registered. The results showed that the opening size and position involved in RC slab had a significant change in the value of natural frequency and period for the high level modes. The material nonlinearity affect on free vibration analysis of RC opening slab with different levels of stiffness modifiers was taken into account. The dynamic characteristics of RC opening slab as a function of stiffness modifier degree was numerically measured for six mode shapes. The paper found that a reduction in stiffness modifier value greatly reduce the .natural frequency of RC opening slab