• Geomechanics and Engineering
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• v.5 no.6
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• pp.595-611
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• 2013

This paper presents a three-dimensional (3D) integrated numerical model where the wave-induced pore pressures in a porous seabed around breakwater heads were investigated. Unlike previous research, the Navier-Stokes equation is solved with internal wave generation for the flow model, while Biot's dynamic seabed behaviour is considered in the seabed model. With the present model, a parametric study was conducted to examine the effects of wave and soil characteristics and breakwater configuration on the wave-induced pore pressure around breakwater heads. Based on numerical examples, it was found that the wave-induced pore pressures at breakwater heads are greater than that beneath a breakwater. The wave-induced seabed response around breakwater heads become more important with: (i) a longer wave period; (ii) a seabed with higher permeability and degree of saturation; and (iii) larger angle between the incident waves and breakwater. Furthermore, the relative difference of wave-induced pore pressure between fully-dynamic and quasi-static solutions are larger at breakwater heads than that beneath a breakwater.

• Earthquakes and Structures
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• v.13 no.5
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• pp.473-484
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• 2017

The objective of this paper is to report on a study of the use of unstiffened thin steel plate shear walls (SPSWs) for the seismic performance improvement of reinforced concrete frames with deficient lateral rigidity. The behaviour of reinforced concrete frames during seismic activities was rehabilitated with an alternative and occupant-friendly retrofitting scheme. The study involved tests of eight 1/3 scale, one bay, two storey test specimens under cyclic quasi-static lateral loadings. The first specimen, tested in previous test program, was a reference specimen, and in seven other specimens, steel infill plates were used to replace the conventional infill brick or the concrete panels. The identification of the load-deformation characteristics, the determination of the level of improvement in the overall strength, and the elastic post-buckling stiffness were the main issues investigated during the quasi-static test program. With the introduction of the SPSWs, it was observed that the strength, stiffness and energy absorption capacities were significantly improved. It was also observed that the experimental hysteresis curves were stable, and the composite systems showed excellent energy dissipation capacities due to the formation of a diagonal tension field action along with a diagonal compression buckling of the infill plates.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.849-854
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• 2002

From the analysis results of some as-built drawings in national roadway bridges in Korea, many bridge piers are expected to show complex shear-flexural behaviour under earthquakes. But the previous research works about the seismic evaluation of bridges considered flexural behaviour RC piers only. In addition, the past bridge design specifications in Korea didn't include limitation on the amount of longitudinal lap splices in the plastic hinge zone of piers. Thus a large majority of non-seismically designed bridge piers in Korea may have lap splices in plastic hinge zone. In this study, prototype pier was selected among existent bridge piers whose failure mode is expected to be complex shear-flexural mode. And then, full scale and 1/2 reduced scale model RC piers with various longitudinal lap splice details were constructed. From the quasi static test results on these model RC piers, the effect of longitudinal lap splices on the seismic performance of bridges piers was analyzed. And the seismic capacity of the non-seismically designed shear-flexural RC piers was evaluated.

• Structural Engineering and Mechanics
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• v.50 no.5
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• pp.589-603
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• 2014

Expressions for determining the value of the impact force as reported in the literature and incorporated into code provisions are essentially quasi-static forces for emulating deflection. Quasi-static forces are not to be confused with contact force which is generated in the vicinity of the point of contact between the impactor and target, and contact force is responsible for damage featuring perforation and denting. The distinction between the two types of forces in the context of impact actions is not widely understood and few guidelines have been developed for their estimation. The value of the contact force can be many times higher than that of the quasi-static force and lasts for a matter of a few milli-seconds whereas the deflection of the target can evolve over a much longer time span. The stiffer the impactor the shorter the period of time to deliver the impulsive action onto the target and consequently the higher the peak value of the contact force. This phenomenon is not taken into account by any contemporary codified method of modelling impact actions which are mostly based on the considerations of momentum and energy principles. Computer software such as LS-DYNA has the capability of predicting contact force but the dynamic stiffness parameters of the impactor material which is required for input into the program has not been documented for debris materials. The alternative, direct, approach for an accurate evaluation of the damage potential of an impact scenario is by physical experimentation. However, it can be difficult to extrapolate observations from laboratory testings to behaviour in real scenarios when the underlying principles have not been established. Contact force is also difficult to measure. Thus, the amount of useful information that can be retrieved from isolated impact experiments to guide design and to quantify risk is very limited. In this paper, practical methods for estimating the amount of contact force that can be generated by the impact of a fallen debris object are introduced along with the governing principles. An experimental-calibration procedure forming part of the assessment procedure has also been verified.

• Computers and Concrete
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• v.12 no.5
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• pp.585-612
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• 2013

The paper presents quasi-static numerical simulations of the behaviour of short reinforced concrete beams without shear reinforcement under mixed shear-tension failure using the FEM and four various constitutive continuum models for concrete. First, an isotropic elasto-plastic model with a Drucker-Prager criterion defined in compression and with a Rankine criterion defined in tension was used. Next, an anisotropic smeared crack and isotropic damage model were applied. Finally, an elasto-plastic-damage model was used. To ensure mesh-independent FE results, to describe strain localization in concrete and to capture a deterministic size effect, all models were enhanced in a softening regime by a characteristic length of micro-structure by means of a non-local theory. Bond-slip between concrete and reinforcement was considered. The numerical results were directly compared with the corresponding laboratory tests performed by Walraven and Lehwalter (1994). The advantages and disadvantages of enhanced models to model the reinforced concrete behaviour were outlined.

• Structural Engineering and Mechanics
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• v.38 no.1
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• pp.27-37
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• 2011

This paper presents the results of a study on the capability of nonlinear quasi-static finite element modelling in simulating the hysteretic behaviour of CFRP and GFRP-retrofitted RC exterior beam-column joints under cyclic loads. Four specimens including two plain and two CFRP/GFRP-strengthened beam-column joints tested by Mahini and Ronagh (2004) and other researchers are modelled using ANSYS. Concrete in compression is defined by the modified Hognestad model and anisotropic multi-linear model is employed for modelling the stress-strain relations in reinforcing bars while anisotropic plasticity is considered for the FRP composite. Both concrete and FRP are modelled using solid elements whereas space link elements are used for steel bars considering a perfect bond between materials. A step by step load increment procedure to simulate the cyclic loading regime employed in the testing. An automatically reforming stiffness matrix strategy is used in order to simulate the actual seismic performance of the RC concrete after cracking, steel yielding and concrete crushing during the push and pull loading cycles. The results show that the hysteretic simulation for all specimens is satisfactory and therefore suggest that the numerical model can be used as an inexpensive tool to design of FRP-strengthened RC beam-column joints under cyclic loads.

• Earthquakes and Structures
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• v.6 no.6
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• pp.627-646
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• 2014

Adobe is one of the oldest construction materials that is still used in many seismic countries, and different construction techniques are found around the world. The adobe material is characterized as a brittle material; it has acceptable compression strength but it has poor performance under tensile and shear loading conditions. Numerical modelling is an alternative approach for studying the nonlinear behaviour of masonry structures such as adobe. The lack of a comprehensive experimental database on the adobe material properties motivated the study developed here. A set of a reference material parameters for the adobe were obtained from a calibration of numerical models based on a quasi-static cyclic in-plane test on full-scale adobe wall representative of the typical Peruvian adobe constructions. The numerical modelling, within the micro and macro modelling approach, lead to a good prediction of the in-plane seismic capacity and of the damage evolution in the adobe wall considered.

• Advances in concrete construction
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• v.2 no.4
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• pp.309-324
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• 2014

In the design of reinforced concrete structural walls, in order to ensure adequate inelastic displacement behaviour and to sustain deformation demands imposed by strong ground motions, special reinforcement is considered while designing. However, these would lead to severe reinforcement congestion and difficulties during construction. Addition of randomly distributed discrete fibres in concrete improves the flexural behaviour of structural elements because of its enhanced tensile properties and this leads to reduction in congestion. This paper deals with effect of addition of steel fibres on the behavior of high performance fibre reinforced cement concrete (HPFRCC) slender structural walls with the different volume fractions of steel fibres. The specimens were subjected to quasi static lateral reverse cyclic loading until failure. The high performance concrete (HPC) used was obtained based on the guidelines given in ACI 211.1 which was further modified by prof.Aitcin (1998). The volume fraction of the fibres used in this study varied from 0 to 1% with an increment of 0.5%. The results were analysed critically and appraised. The study indicates that the addition of steel fibres in the HPC structural walls enhances the first crack load, strength, initial stiffness and energy dissipation capacity.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.323-328
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• 2002

The 1995 devastating Hyogoken-Nambu earthquake sent mental shock waves that awakened the public concern about the seismic performance of infrastructures in Korea. Seismic safety of reinforced concrete bridge piers could be secured through sufficient strength and stiffness of longitudinal steels and confined core concrete, and through ductile behaviour of bridge piers in the inelastic range. This study has been performed to verify the effect of lap spliced longitudinal steel for the seismic behavior of reinforced concrete bridge piers. Quasi-static test has been done to investigate the physical seismic performance of RC bridge piers, such as displacement ductility, energy absorption etc.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.823-828
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• 2002

Lap splice in plastic hinge region of RC bridge piers is inevitable because of the constructional joint between footing and column. RC circular columns with lap-splice in plastic hinge region are widely used in Korean highway bridges. It is, however, believed that there we not many experimental research works for nonlinear behavior of these columns subjected to earthquake motions. This study has been peformed to verify the effect of lap splice and confinement steel ratio for the seismic behaviour of reinforced concrete bridge piers. Quasi-static test have been done to investigate the physical seismic performance of RC bridge piers, such as displacement ductility.