Seismic Mitigation of Curved Continuous Girder Bridge Considering Collision Effect

Due to structural irregularity, curved bridgesaremore likely to cause non-uniform collisions and unseating between adjacent components when subjected to earthquakes. Based on the analysis of the collision response of curved bridges duringearthquakes, and according to the seismic characteristics of curved bridges, research was carried out on pounding mitigation and unseating prevention measures. A curved bridge with double column piers was taken as an engineering example, and a finite element model of curved bridges thatcould consider the non-uniform contact collision between adjacent components was built with ABAQUS software. Viscoelastic dampers, viscous dampers, and a lead rubber bearing were selected as the damping devices, and a steel wire rope-rubber mat was used as the pounding mitigation device to form the combinatorial seismic mitigation system. Based on the principle of energy dissipation combined with constraints, three kinds of combined seismic mitigation case were determined; a seismic response analysis was then performed. The results indicated that the three kinds of combined seismic case were effective atreducing the response topounding force, stress, damage, girder torsion and displacement, and achieved the goals of seismic mitigation and unseating prevention.

Modelling lead-rubber seismic isolation bearings using the unified mechanics theory

Lead-rubber seismic isolation bearings (LRB) have been installed in a number of essential and critical structures, like hospitals, universities and bridges, in order to provide them with period lengthening and the capacity of dissipating a considerable amount of energy to mitigate the effects of strong ground motions. Therefore, studying the damage mechanics of this kind of devices is fundamental to understand and accurately describe their thermo-mechanical behavior, so that seismically isolated structures can be designed more safely. Hitherto, the hysteretic behavior of LRB has been modeled using 1) Newtonian mechanics and empirical curve fitting degradation functions, or 2) heat conduction theories and idealized bilinear curves which include degradation effects. The reason for using models that are essentially phenomenological or that contain some adjusted parameters is the fact that Newton’s universal laws of motion lack the term to account for degradation and energy loss of a system. In this paper, the Unified Mechanics Theory – which integrates laws of Thermodynamics and Newtonian mechanics – is used to model the force-displacement response of LRB. Indeed, there is no need for curve fitting techniques to describe their damage behavior because degradation is calculated at every point using entropy generation along the Thermodynamics State Index (TSI) axis. A finite element model of a lead-rubber bearing was constructed in ABAQUS, where a user material subroutine UMAT was implemented to define the Unified Mechanics Theory equations and the viscoplastic constitutive model for lead. Finite element analysis results were compared with experimental test data.

Reducing the lateral displacement of lead rubber bearing isolators under the near field earthquakes by crosswise dissipaters connected to rigid support structure

The purpose of base isolation is to absorb earthquake energy, prolong the life of the structure, and enable the structure to be similar to a rigid body. However, since resonance can occur due to the closeness of the period of structures to the long period and large velocity pulses of the near field earthquakes, the stability of these buildings greatly reduces, and with the large displacement above isolation level, sometimes, tendency of overturning is created in isolators leading to their destruction. The main objective of this study is to significantly reduce the lateral displacement of base isolation subjected to near field earthquakes. In this research, seismic response calculation has been carried out for five steel moment frame structure with the 3, 5, 8, 11, and 14 stories in two states of with and without stiff core structure and energy dissipaters. The analyses has been done under fourteen scaled records of seven near-source and seven far-source earthquakes. It has been shown that the lateral displacement of base isolation system can be reduced by 87% for low-rise buildings, and 77% for high-rise buildings.

Structural Control Using LRB in Irregular Building

Earthquakes are measure as one of all nature’s greatest hazards; throughout the historic time they need to cause important loss of life and severe harm to property, particularly to man-made structures. On the opposite hand, earthquakes offer architects and engineers a variety of vital criteria foreign to the traditional style method. during this analysis paper study, base isolation as an associate degree earthquake resisting style technique was used that well dissociate a construction from its substructure and increase flexibility resisting on the bottom vibration areas by providing the isolators. Lead rubber bearing (LRB) isolator could be a passive structural vibration management technique. during this analysis study, unstable behavior of irregularity building in the simple model, re-entrant corner plan irregular model, mass irregular model, and stiffness irregular model are measure configurations with varied frame sections with and while not LRB base isolation was analyzed for the comparative analysis on the idea of base shear, storey shear, stoery displacement, storey drift and storey acceleration with 3 earthquake information, first is Bhuj earthquake, second is Kobe Japan earthquake, and third is Loma Prieta earthquake analysis is done by E-TABS 18.0.20software. Non-linear time history analysis and for design purpose of a base-isolated system and for seismic design of isolated structure consistent with IS 1893 (part 1):2016 and UBC 1997.

The Behavior of Elevated Water Tanks under Impact Loading

Because of the crucial role of elevated water tanks and their various uses, it is necessary to evaluate their structural behavior under threats to improve the durability performance of such tanks without putting them in jeopardy. In the present research, three open cylindrical concrete water tanks were modeled under an impact load (aerial blast) with the weight of 100 kg TNT explosive charge. The tanks were modeled in 3 forms: slender, middle, and broad (Aspect ratio = 1.28,1 and 0.85). Each tank contained various levels of water (non-water, half water, and full water) to estimate their structural behavior under blast loading. Moreover, the CEL (Coupled Eulerian-Lagrangian) approach was used to simulate water structure interaction in finite element program. For a comprehensive analysis of the structural behavior of water tanks, LRB (Lead rubber bearing) isolator device was also used to observe the effect of isolator under blast loading on elevated water tanks in all models. The results of this study show that the water level leads to stiffness of the structures that cause better performance under blast loading and also the intersection of the shaft and concrete column would be the critical section of this structure under blast loading. It is also concluded that Stress and Strain decrease as the water tanks level increase and stiffen (up to 33 %). Also, it is noticeable that the existence of the isolator has deteriorated the results because of the decreases in the structure’s stiffness and the increase of the displacements.

Seismic Performance of Steel Framed Building With Mass Irregularities With The Use of Different Combinations of Base Isolators and Dampers

This study addresses the nonlinear seismic responses of 3D Steel frame building upgraded with a series of passive protective systems. To this, friction damper (FD) as an energy dissipation device and lead rubber bearing (LRB), and friction pendulum bearing (FPB) base isolators are considering. For this purpose, eight different cases are taken into account. The first case contains a ten-story steel frame regular compare with irregular buildings (mass irregularities) as fixed-base (FB), the other four cases are the single use of FD, LRB and FPB in such frame, and the last three cases are the combined use of FD with LRB and FPB, Combination of isolators LRB and FPB, Combination of LRB, FPB and FD. Above same cases are considering for fifteen story steel frame regular buildings compare with irregular buildings (mass irregularities). Two ground motion records considering in this study by non-linear time history analysis in ETABS.

Two-Stage Optimization Method for the Bearing Layout of Isolated Structure

Design of seismic isolated building is often a highly iterative and tedious process due to the nonlinear behavior of the system, a large range of design parameters, and uncertainty of ground motions. It is needed to consider a comprehensive optimization procedure in the design of isolated buildings with optimized performances. This can be accomplished by applying a rigorous optimization technique. However, due to many factors affecting the performance of isolated buildings, possible solutions are abundant, and the optimal solution is difficult to obtain. In order to simplify the optimization process, an isolated building is always modeled as a shear-type structure supported on the isolated layer, and the optimal results are the parameters of the isolated layer which could not be used as a practical design of the isolated structure. A two-stage optimization method for designing isolated buildings as a practical and efficient guide is developed. In the first stage, a 3D isolated building model is adopted that takes into account of nonlinear behavior in building and isolation devices. The isolation devices are simplified as a kind of lead-rubber bearing. The genetic algorithm is used to find the optimal parameters of the isolated layer. In the second stage, the location parameters of isolation bearing layout are optimized. Moreover, the cost of the isolation bearing layout should be as low as possible. An integer programming method is adopted to optimize the number of each type of isolator. Considering vertical bearing capacity of isolators and the minimum eccentricity ratio of the isolated layer, the optimal bearing layout of the isolated building can be obtained. The proposed method is demonstrated in a typical isolated building in China. The optimum bearing layout of the isolated building effectively suppresses the structural seismic responses, but the cost of the isolated layer might slightly increase.