Asian journal of civil engineering
Volume:14 Issue: 1, Feb 2013

Sealed tuned liquid column gas dampers, i.e. with a gas spring effect taken into account, TLCGD, are ideally suited to increase the effective structural damping of bridges when vibrating in the critical low frequency band. The evident features of this type of absorbers are no moving mechanical parts, cheap and easy implementation, low maintenance costs and simple modification of the natural frequency, and even of the damping properties (by means of built-in orifice plates). Modal tuning in the design stage by means of the analogy to the classical mechanical damper of the spring-mass-dashpot type, TMD, is subsequently followed by fine-tuning in state space, rendering the absorber parameter (frequency and damping) optimal and, when designing smaller units in parallel action, yields the control even more robust. The equilibrium gas-pressure is the main control parameter to optimize the absorber frequency when the volume of the individual gas vessel above the liquid gas interface is properly selected. U- or V-shaped TLCGD with horizontal extension maximized, are proposed to reduce dominating horizontal vibrations of long-span bridges (including pedestrian bridges) and, as worked out in detail, in the case of the cantilever method of bridge construction, to increase the allowable maximum length of the cantilever, despite of wind-gusts. An alternative design, VTLCGD provides the control force vertically, and thus counteracts dominating vertical, traffic-induced vibrations. Sealing of the piping system in that case is a necessary condition since an equilibrium gas-pressure difference is essential for the vertical action of the displaced fluid. The horizontal length of this absorber is kept to a minimum. Illustrative examples are described to convincingly approve the un-revealed action of the liquid absorber.

This study evaluates seismic reliability of RC framed buildings with two different lateral load resisting systems. Four example buildings with different heights and different lateral load resisting systems are analyzed through incremental dynamic analysis under two sets of ordinary and near-fault records. A vector-valued intensity measure is used for reliability evaluation. The results of case studies show that in near-fault ground motions there is a slight difference between seismic reliability of MRF and dual systems, particularly for highrise buildings. In contrast, adding shear walls improves seismic reliability of both of lowrise and high-rise buildings in ordinary ground motions.

The use of bamboo as a structural construction material is gaining traction primarily because (i) it is a rapidly growing material and thus sustainable, and (ii) it has many positive engineering attributes such as its high strength-to-weight ratio in tension. One area of recent development has been the use of bamboo-based construction in seismically active regions of India. In this paper the seismic behaviour of one type of bamboo-based construction isexamined and validated by calibrating a non-linear numerical model to wall panel experimental results, and then performing multi-record incremental dynamic analysis (IDA) on the full system level model. The response was very reasonable due, in part, to the relatively light weight of the bamboo roof system. Most importantly, the damage to the bamboo-mortar walls during testing, and particularly the eventual failure mechanisms, were consistent with modern engineered materials thus confirming that this type of construction is a viable alternative for seismic regions, particular in developing countries.

A new innovative Hydro-pneumatic Semi-active Resettable Device by using MR-Fluid (MR-HSRD) is introduced for vibration suppression of structures. The novel device consists of a cylinder-piston system with control valve and magneto-rheological valve (MR valve) mounted on a bypass pipe connecting two sides of the cylinder. The MR-HSRD is set by changing the stiffness and the damping of the device independently. Moreover, the hysteresis behavior can be adjusted by using different control logics for control valve. A mathematical model is presented for behavior of the device. The experimental results of MR-HSRD under cyclic and static loadings are presented and are compared with the mathematical models.

This paper investigated the use of mini slump cone test along with the graduated glass plate to obtain the optimization of Superplasticiser (SP) and Viscosity Modifying Agent (VMA) in self compacting mortar (SCM). The SCM mixes had 35% replacement of cement with class F fly ash and water/cementitious ratios by weight (w/cm) 0.32 and 0.36. It is observed that for the same cementitious proportions, the optimum dosage of SP was the same for the mixes having w/cm 0.32 and 0.36. Mortar mixes with w/cm 0.36 showed an increase in the rate of flow i.e., lower viscosity at each level of SP dosage as compared to that of mixes with w/cm 0.32. It is also observed that minimum dosage of VMA was required to use in the mortar mixes having w/cm 0.36 in order to arrest the bleeding. Whereas, the use of VMAdosage was not required to use in the mortar mixes having w/cm 0.32 as no bleeding was observed at the optimum dosage of SP. Practically, it is seen that mini slump cone test is the best choice for SCM tests to evaluate the mortar spread and its viscosity (T20). Also, it is seen that percentage of sand in mortar doesn’t affect the optimum dosage of SP (saturation point) when the cementitious proportions are kept the same.

The paper presents the results of a study on the ductility behavior of composite fibre reinforced polymer- high strength concrete columns under uni-axial compression. The columns had slenderness ratios of 8, 16, 24 and 32. Three types of wrap materials (Chopped Strand Mat GFRP, Uni-Directional Cloth GFRP and Woven Roving GFRP) were used with 3 mm and 5 mm thicknesses. The columns were tested under monotonic axial compressive loading up to failure. The deflections and axial strain were noted for each load increment. The HSC columns with GFRP wrapping exhibited improved performance in terms of deflection ductility and energy ductility capacity. Regression equation has been proposed for predicting the performance parameters. A better correlation has been observed between the test results and those predicted through the proposed equations.

In the present paper, an investigation is made to study the effect of maximum size of aggregate in higher grade concrete using high volume fly ash. Three different mixes of M50 grade concrete were designed using graded coarse aggregate of three maximum sizes of 10mm, 12.5mm and 20mm. And for each mix, cement was replaced with fly ash at 0%, 10%, 20%, 30%, 40% and 50% (%replacements). All the mixes were cured for 56 days and tested for compressive strength, flexural strength and splitting tensile strength. The test results obtained have suggested that the maximum size of coarse aggregate in M50 grade concrete at various replacement levels of fly ash was 12.5 mm aggregate and optimum replacement of fly ash was 30%. The percentage increase was 20% for compressive strength, 20% for splitting tensile strength and 5% for flexural strength when compared to the design strength.

Dam-water-foundation rock interaction effects on linear and nonlinear earthquake response of arch dams are investigated. For this purpose, the dam-water-foundation rock system subjected to earthquake ground motion is idealized using the finite element method involving the materially and geometrically nonlinear effects. A real world arch dam is considered and the dam is analyzed for various conditions of interaction problem for both linear and nonlinear behaviors. Numerical results indicate that the dam-water-foundation rock interaction with a materially nonlinear behavior affects the arch dam response significantly and they should be included to achieve a safe design for arch dams.

The paper offers an exact, closed form solution for performance-based elastic-plastic design of moment frames under lateral loading. It introduces the concept of uniform response, which in turn, enables the engineer to manually define, predict and to control structural response at pre-selected design stages, such as before and at first yield, any fraction of the failure load or specified drift ratio, up to and including incipient plastic collapse. It is assumed that the moment frames are composed of imaginary, symmetric, rectangular modules that are stacked on top of each other to form vertical subframes of uniform response where individual modules are designed to deform identically and to develop internal stresses of equal magnitude simultaneously throughout the subframe. These subframes respond as structures of uniform strength and stiffness in which members of the same group such as beams and columns, share the same demand-capacity ratios regardless of their location and number of similar elements within the framework. The subframes are eventually integrated to reconstruct the original system. The proposed solutions are unique since they satisfy the prescribed yield criteria, static equilibrium as well as the boundary support conditions. While moment frames of uniform response are ideally suited for preliminary performance control studies, the method is further enhanced by the introduction of moment control factors. These factors are used to control the propagation of plasticity within the structure and symbolize the formation or elimination of plastic hinges as needed. In practical terms, cover plates, reduced beam sections or similar technologies may be used to avoid and/or to induce formation of plastic hinges in selected locations. The proposed drift control and moment modification equations appear to be the only ones of their kind that can analytically estimate the lateral displacements and element moments of such frames, including the P-delta effects, throughout the history of loading of the structure.

Composite steel shear wall is a lateral load resisting system that consists of steel plate as a primary component with concrete wall (cover) attached to one side or both sides of the plate to prevent it from elastic buckling. The composite action of the system is ensured by using high-strength bolts. This paper investigates the effects of the distance between bolts on the behavior of the system. For this purpose, 14 one story one bay specimens with various distances between bolts were modeled and analyzed in the finite element software ABAQUS. To verify the ability of the model, numerical results were compared with a valid experiment, which shows very good agreement. Results demonstrate that increasing distance between bolts would improve the seismic behavior of the system. However, this increase in distance should be limited, since permission to widespread buckling of steel plate in free subpanels between bolts would result in no more improvement of the behavior. By comparing the results in elastic region, it was clearly observed that the initial stiffness of the system is not affected by changing the distance between bolts.

A large inventory of older masonry buildings exists in earthquake-prone regions. The majority of these buildings were built before any provisions for earthquake loading were established. Several seismic retrofitting techniques for masonry structures have been developed and practiced and fiber reinforced polymer (FRP) material has been increasingly used owing to its high strength/stiffness to mass ratio and easy application. This paper presents a finite element modeling approach, developed with commercial software, for the analysis of the behaviour of unreinforced and FRP strengthened perforated brick shear wallswhen they are subjected to a combination of vertical compression preload and in-plane cyclic shear loading. The numerical simulations are compared with experimental data andthe accuracy of the proposed finite element model is validated. Finally, effects of different strengthening configurations with FRP on the in-plane cyclic performance of brick walls with openings (e.g. door, window) having different aspect ratios and positions are examined.