RC造柱梁部分架構の柱曲げ強度増大を図るための外付け補強法とその実験検討

Experimental and numerical study on the residual seismic performance of post-blast RC piers

This paper presents the results of a static lateral loading test performed on a traditional timber farmhouse in Japan. The aim of this research is to clarify the horizontal load carrying capacity and the failure mode of this type of house by full-scale experiment. The house is situated in Yamaguchi prefecture, which is in the southwestern part of Japan, and was built in the late 18th century. The experiment was performed by placing static loading equipment within the house, and placing two reaction supporting systems outside the house. A lateral cyclic loading test was carried out and the maximum lateral load and the failure mode were determined. Static analysis using a theoretical mud wall model was also performed. The results of this analysis are discussed in comparison with those of the experiment.

Seismic response and failure mechanism of ordinary concrete and UHTCC short columns reinforced with negative Poisson's ratio steel bars

Seismic behavior of precast concrete beam-column joints with encased steel tube

The beam-column joint is an important component of Reinforced Concrete (RC) structures because its design and detailing are critical to the safety of these structures under seismic loading. In recent decades, structural behaviour of beam-column joints has been widely explored. To better understand the behaviour of beam-column joints, researchers have conducted experiments and provided analytical and experimental solutions. The seismic behaviour of beam-column joints with and without Glass Fibre Reinforced Polymer (GFRP) when subjected to quasi-static lateral cyclic loading was compared in this research using two specimens. The first specimen is a typical RC exterior beam-column joint without GFRP while the second specimen is RC exterior beam-column joint that is pre-installed with Glass Fibre Reinforced Polymer (GFRP) using Near-Surface Mounted (NSM) technique. The specimens were evaluated to a drift of 2.0% under quasi-static lateral cyclic loading. There were two cycles in each drift. Based on the amplitudes of both specimens, it can be seen that the amplitude of beam-column joint with GFRP is lower than the beam-column joint without GFRP. This suggests that the presence of GFRP reduces the intensity of the loading. This study also discusses the energy dissipation and equivalent viscous damping on both specimens. During the experiment, each crack, void between the concrete, and spalling of concrete fragments were carefully monitored. Visual observation during the experiment shows that severe cracking is evident on the inner part of the structure in both specimens. Therefore, a new location of GFRP-NSM would be suggested for a future experiment.

In the present study, the seismic performance of structural walls with boundary elements confined by conventional tie hoops and steel fiber concrete (SFC) was investigated. Cyclic lateral loading tests on four wall specimens under constant axial load were performed. The primary test parameters considered were the spacing of boundary element transverse reinforcement and the use of steel fiber concrete. Test results showed that the wall specimen with boundary elements complying with ACI 318-11 21.9.6 failed at a high drift ratio of 4.5% due to concrete crushing and re-bar buckling. For the specimens where SFC was selectively used in the plastic hinge region, the spalling and crushing of concrete were substantially alleviated. However, sliding shear failure occurred at the interface of SFC and plain concrete at a moderate drift ratio of 3.0% as tensile plastic strains of longitudinal bars were accumulated during cyclic loading. The behaviors of wall specimens were examined through nonlinear section analysis adopting the stress-strain relationships of confined concrete and SFC.

Experimental study on seismic behavior of fabricated lightweight steel solid waste High-strength foam concrete composite wall

Cyclic loading tests of RC columns strengthened with high ductile fiber reinforced concrete jacket

A steel–concrete composite wall with boundary elements of steel U-section was developed for high structural performance and efficient use of materials. Cyclic lateral loading tests were performed on the proposed walls to investigate the flexural and shear performances. The test parameters included the failure mode of specimens, type of boundary reinforcement, sectional area of steel U-sections, horizontal web reinforcement ratio, and wall thickness. In the flexural yielding specimens, the flexural strengths of the proposed walls were equivalent to those of conventional reinforced concrete (RC) walls with boundary elements of vertical rebars, even though the yield strength of steel plates was 24% less than that of rebars. Further, the use of steel U-sections increased displacement ductility and energy dissipation, providing lateral confinement to the boundary concrete and restraining shear cracking and sliding. In the shear failure-mode specimens, the use of steel U-sections increased the diagonal tension-shear strength of walls. Thus, the shear strength of the composite walls was greater than that of conventional RC walls. The existing design method of JGJ 138 reasonably predicted the shear strength of the proposed composite walls, considering the contribution of boundary steel U-sections.

This paper presents experimental results from three prestressed precast concrete walls in comparison with a conventional reinforced concrete (RC) wall. The prestressed specimens utilise a combination of high-strength post-tensioned (PT) steel and mild reinforcing steel for lateral resistance, whereas the RC specimen retains a conventional code-compliant design. The major advantage of the prestressed specimens incorporating PT steel is a self-centring capability after a large lateral excursion. At the same time, PT steel facilitates construction by post-tensioning and connecting wall panels together. In this study, all the test walls had an identical overall geometry and were tested under the same reversed cyclic lateral loading. Comparisons of the seismic performance of prestressed and RC specimens were made in relation to progression of damage, failure mechanism, strength and drift capacity, energy dissipation and residual drift. The PT steel and base joint behaviours of the prestressed specimens were also recorded. Results show that the prestressed precast concrete walls feature minimal structural damage and excellent self-centring tendency compared to their RC counterpart; these features are essential to achieve a resilient structural system for use in seismic regions.

An innovative technique to improve the capacity of piles installed in soft clayey soils using high-voltage electrokinetics was investigated in the present study. A largescale testing facility was established to execute the treatment and perform loading tests on the model piles. Eight steel pipe piles were installed in two identical cylinders filled with simulated marine sediment. Five electrically insulated electrodes were installed close to the piles to develop a non-uniform electric field in the test cylinder. Negative DC voltages of −20, −30 and −10 kV were applied in three phases for 33 days in the treatment cylinder. Lateral and cyclic lateral loading tests were performed, and the results were compared for both cylinders after each phase of treatment. The pile response was presented in terms of the experimental load–deflection curves. It was observed that the lateral capacity increased 81, 60 and 12% after the first, second and third treatment phases, respectively. The pile stiffnesses increased, and the displacements at the peak amplitude of the cyclic load decreased, due to the treatment. The improvement in the cyclic performance of the piles was evaluated in terms of the change of the soil degradation factors. The soil degradation factor increased 4·6, 14·6 and 2% after the first, second and third treatment phases, respectively.

This study is concerned with evaluating the response of single pile subjected to cyclic horizontal uniaxial loading. Combination of lateral cyclic loading and constant vertical or lateral load in two-orthogonal directions is also studied. Moreover, the influence of one- and two-way loading, number of cycles and the intensity of constant load in conjunction with the cyclic lateral load is presented. The study is further continued by comparing the performance of long and short single pile embedded in clayey soil. A series of three-dimensional finite element models using ANSYS code are conducted to model three-dimensional transient analysis as well as the complicated soil pile interaction. In order to verify the validity numerical model, the numerical response is compared with reported results obtained by experimental cyclic load test performed on single pile penetrated in soft clay. Results show strong coupling between the two-orthogonal direction of lateral loading that decreases the lateral pile capacity. The interaction relation of biaxial loading with the factor b = 1.2 and 1.15 for one- and two-way loading respectively may well approximate the analysis results. The results of study are presented in terms of lateral cyclic capacities, pile head deflection, displacement profile and bending moment over the pile length.

The effects of earthquakes can be devastating especially to existing structures that are not based on earthquake resistant design. This study proposes a steel grid shear wall that can provide a sufficient lateral resistance and can be used as a seismic retrofit method. An experiment was performed on reinforced concrete (RC) frames with and without the steel grid shear wall proposed in this study. These frame specimens were subjected to combined axial and cyclic lateral loads that were applied by using two actuators with a maximum capacity of 500 kN and a single actuator with a maximum capacity of 2,000 kN, respectively. The experimental results showed that the RC frame specimen with the proposed shear wall retained high lateral strength and ductility.

Three identical half-scale of exterior beam-column joints of RC buildings with different arrangement of connections detailing are designed, constructed and tested under reversible vertical cyclic loading. Each set consists of reinforced concrete beams, column and foundation beam which represents the exterior joints of the ground floor of RC buildings. The objectives of this study are to examine seismic performance, to observe visual damages and to classify different types of damages which occur in beam-column joints. The first set is designed beam-column joint in accordance to BS 8110 where no anchorages of bars are tied between beam and column. Second set comprises of three anchorage bars from column are placed and tied with top of reinforcement bars in the beam. Third set is designed with cross-bracing of reinforcement bars at the intersection of beam-column joint. Results showed that the beam-column connections which designed according to BS 8110 without anchorage bars suffer the most severe damages as compared to connections with anchorage bars and cross-bracing bars. Beam-column joint with cross-bracing bars experienced less damage as compared to two types of joints. Visual structural damages of beam-column joints include cracks prorogation, the spalling of concrete shell, buckling of longitudinal reinforcement bars and fractured of shear reinforcement bars. Therefore, it is an appropriate time to revise and replace the current code of practice to seismic code so that reinforced concrete buildings which are constructed in Malaysia are save under long-distant earthquake excitation and local earthquake.

Beam–column joints in concrete buildings are critical for structural integrity under earthquake loading. Thus, accurate beam–column joint nonlinear models are important in seismic assessment and design of buildings. Most joint models in the literature are deterministic; the majority of which either are based on a small data set or do not distinguish failure modes and types of joints. This paper presents a data-driven probabilistic nonlinear model for concrete beam–column joints with transverse reinforcement. The model is based on multilinear regression using a newly developed database of 395 reinforced (confined) joints. Based on this database, current US seismic assessment provisions for beam–column joints were found to be conservative and have inconsistent levels of probability of exceedance for various nonlinear modeling parameters. The proposed probabilistic model unifies the level of probability of exceedance at 50%, a level that is consistent with the recently updated nonlinear beam and column provisions to avoid the bias in nonlinear assessment procedures. The proposed model exhibited good correlation with the test database, validation data sets, and cyclic backbones curves. Improved performance-based seismic design accuracy and economy for ductile concrete frames may result if current seismic assessment standards are updated based on the proposed model.