Results Of Cyclic Loading Tests Research Articles

Damage Evolution Equation Reflecting Hydrostatic Pressure Effect and Its Application to Concrete Slabs under Projectile Impact

In this study, triaxial cyclic loading and unloading compression tests were performed on concrete specimens under six confining pressures (0, 5, 10, 20, 30, and 40 MPa). The elastic modulus was reduced to characterize the damage, and the damage-plastic strain relationships under different confining pressures were determined. The results showed that the damage evolution rate declined significantly as the confining pressure increased. The experimental results of the uniaxial-tension cyclic loading and unloading tests were combined to derive a damage evolution equation that reflected the hydrostatic pressure effect, and the material parameters were determined by using experimental data. Finally, the derived damage evolution equation was embedded into the Holmquist-Johnson-Cook model and applied to numerical simulations of a concrete slab under projectile impact. The results indicated that the modified Holmquist-Johnson-Cook model can accurately explain the damage evolution process of a concrete slab under projectile impact. Thus, the proposed equation can describe the damage evolution processes of concrete slabs under both impact compression and tension.

Assembled self-centering energy dissipation braces and a force method-based model

A pre-pressed spring self-centering energy dissipation (PS-SCED) bracing system has significant energy dissipation and re-centering abilities, although many welds result in a lengthy manufacturing process and reduce the machining accuracy to an unacceptable level. An assembled pre-pressed spring self-centering energy dissipation (A-PS-SCED) bracing system that uses disc spring groups to provide a re-centering ability and a friction device to dissipate energy, is presented in this paper to simplify production and maintenance. A novel force method-based (FMB) hysteretic analysis model governing the distribution of the internal force is proposed and verified by a numerical model of the A-PS-SCED brace and tests of the PS-SCED brace specimen. The simulation results indicate that the A-PS-SCED brace exhibits sufficient and steady energy dissipation and re-centering capacities. The FMB model agrees well with the numerical model with a maximum bearing force difference of 2% and has steady hysteretic responses under random excitations. The FMB model is used to determine the mechanisms of the stiffness and contact status change during a typical loading process. Additionally, the FMB model accurately predicts the cyclic loading test results of an existing PS-SCED brace specimen, and the average bearing force differences are 6% and 2% at friction force of 200 kN and 300 kN, respectively.

Lateral force-displacement response of rat-trap bonded masonry

Rat-trap bond (RTB) masonry is one of the most economical, fast, and energy efficient construction technique for brick masonry buildings. Many developing countries including India, Nepal, Sri Lanka and Pakistan have constructed large number of buildings using this technique. However, structural stability and performance validation are as important as the economy in any construction project. Therefore, this study presents the results of in-plane quasi-static cyclic load tests on three wall specimens constructed in RTB. The pre-compression load was adjusted to simulate the load condition of a typical two storey building. The key parameters evaluated include stiffness, ductility, damping, energy dissipation, force-displacement behaviour, lateral strength, etc. The experimentally obtained results were also compared with the existing research of similar nature on conventional masonry as well as with the results predicted by various empirical equations. The comparison indicates that the lateral strength and stiffness of rat-trap masonry is significantly less than those of conventional masonry because of the reduced effective thickness, while other properties like ductility, damping and energy dissipation do not show any significant variation.

Adaptability of polyurethane/water glass grouting reinforcement to subsea tunnels

Polyurethane/water glass (PU/WG) is an organic–inorganic hybrid grouting material used in underground engineering. However, its adaptability to subsea tunnels remains poorly investigated. In this study, curing time, hardening time, seawater influence, strength growth, and cyclic loading tests of PU/WG as well as scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and Fourier transform infrared spectroscopy characterizations were performed. The typical curing and hardening times of PU/WG were 2.02 and 2.49 min, respectively. The strength of the material developed fully when the sample was aged for 2 h. The peak strength and strain were respectively reduced up to 10.9% and 19.6% at the most owing to seawater corrosion. The minimum strength and minimum strain were of 37.7 MPa and 26.9%, respectively. The cyclic loading test results confirmed the high fatigue resistance of the PU/WG material. PU/WG is an ideal reinforcement grouting material for subsea tunnels.

SEISMIC ANALYSIS OF STEEL-CONCRETE COMPOSITE FRAME STRUCTURES BASED ON THE ULTIMATE BALANCE THEORY

A simplified analysis method of steel-concrete composite frame structures under rare earthquake action is established based on the ultimate balance theory. The failure mechanism of composite frames is determined by theoretical analysis and experimental phenomena. Based on the ultimate balance theory and according to the distribution law of the deformation and internal force when the structure reaches the ultimate strength under earthquake action, the seismic strength of the composite frames is calculated when the top horizontal displacement of the frame is equal to H/50, H/40 and the lateral displacement corresponding to the limit load. The calculation results agree well with the low cyclic loading test results of 19 composite frames at home and abroad. It shows that the method can effectively predict the seismic strength of composite frame structures under rare earthquakes. A simplified method is proposed to control the deformation capacity and seismic strength of the composite frame at the same time to make the structure meet the seismic requirement under rare earthquakes.

Bayesian Theory-Based Seismic Failure Modes Identification of Reinforced Concrete Columns

ABSTRACT The aim of this research is to develop a probability method that can identify the flexure, shear or flexural-shear failure of RC columns. A total of 336 columns of cyclic load test results were collected, and a probabilistic model was constructed using the Bayesian procedure. Then, the model was simplified by Bayesian updating. The boundaries for each failure mode were selected through an internal search optimization. The results show that the Bayesian methodology can accurately predict the seismic failure modes of RC columns and the comparison of the identification with other methods underscore the validity of Bayesian method.

Experimental behaviour of non-seismical RWS connections with perforated beams under cyclic actions

The use of perforated (in particular cellular and castellated) beams has become widespread as their manufacturing processes keep minimising wasted material and has become cost-effective by reducing self-weight of steel structures, while allowing for larger clear spans. Although their behaviour to time-invariant vertical loads has been extensively investigated and validated in laboratory setups, their response to reversible actions has not been explored to the same extent. This paper presents results of cyclic load tests of beam-column reduced web section (RWS) connections, considering setups representative of what is observed in low-rise buildings in the UK; a region with sparse seismicity. Results show that RWS connections on these frames can achieve stable hysteresis loops without significant strength degradation, due to the simultaneous occurrence of yielding of the critical cross-section and development of a Vierendeel mechanism on the edges of the perforations (web openings). Also, inelastic action is mostly observed within the beam, thus being successful in protecting the beam-column connection. Performance particularly exceeds what is observed for a benchmarking RBS connection styled according to the same underlying assumptions, hinting that RWS connections could be a more suitable solution for structural retrofitting in regions where seismicity is sparse.

Influence of the specimen production and preparation on the compressive strength and the fatigue resistance of HPC and UHPC

The results of tests under monotonically increasing load and cyclic compression load are often analysed by means of probabilistic methods. Although there is a considerable scattering in the results, especially in the number of cycles to failure, the cause of these cannot be completely explained. The imperfections of the specimens tested are among the causes of this scattering mentioned in the literature. Based on a round robin test the influence of HPC and UHPC production and specimen preparation techniques on the mean values of the compressive strengths, number of cycles to failure and data scattering have been evaluated. The main findings of the study are that the production techniques have an influence on the compressive strength, however, do not affect the mean number of cycles to failure. Moreover, the accurate preparation of the specimens has a positive influence on the compressive strength and the scattering of the results of both compression and cyclic load tests. The mean number of cycles to failure of HPC specimens is not influenced by the preparation techniques, whereas the polishing technique may have a positive influence on the mean number of cycles to failure of UHPC specimens.

The Influence of Fracture Strain Energy on the Burst Tendency of Coal Seams and Field Application

Coal is typically considered a special engineering rock mass because of its low strength, high internal fracture development, good permeability, and random distribution of microparticles and fractures. The results of cyclic loading and unloading tests indicate that the strain energy during the coal deformation process can be divided into three parts: plastic strain energy; fracture strain energy; and base-material strain energy. The energy composition ratio differs depending on coal strength. Lower proportions of fracture strain energy are associated with higher elastic energy indexes, and there is a negative correlation between fracture strain energy and other coal burst tendency indexes. The results were applied on the 4206 isolated island working face of coal mine A in Yan’an, Shanxi, China, yielding good benefits. The findings presented here provide a theoretical basis for understanding the principle of coal seam bursting and guidance for reducing burst risks.

Simplified Plastic Hinge Model for Reinforced Concrete Beam–Column Joints with Eccentric Beams

In nonlinear analysis for performance-based design of reinforced concrete moment frames, a plastic hinge spring element is predominantly used in order to simply and accurately describe the inelastic behavior of beam–column joints, including strength degradation. Although current design codes and guidelines provide various beam–column joint models, the focus is on concentric beam–column joints. Therefore, more studies are required for eccentric beam–column joints, which are also common in practice. In the present study, to consider the effect of beam eccentricity on the behavior of beam–column joints, a simplified plastic hinge model was proposed using the effective joint width of current design codes. The proposed model was compared to the cyclic loading test results of beam–column joints with/without beam eccentricity. The comparison showed that the simplified plastic hinge model with the effective joint width of NZS 3101-2006 or Eurocode 8 is considered acceptable for design purpose.

Evaluation and fitting of a numerical model for reinforced concrete thin walls through experimental results of monotonic and cyclic loading tests

Reinforced concrete thin walls buildings have become one of the most common alternatives for housing construction in Colombia. However, some studies on this system have reported that walls have a limited deformation capacity and may suffer brittle failures. In this paper, a numerical model developed in OpenSees was used to represent the behavior of thin and slender reinforced concrete walls. The model was evaluated and fitted with the experimental response of two representative walls of this type of construction in high seismic hazard zone, in addition to the results of cyclic tests of other investigations with walls of similar characteristics. The experimental response of the walls indicated that, despite reaching a moderate deformation capacity, for the 1% drift limit, the level of damage was severe and lost 77% and 67% of their initial stiffness, respectively, which confirms that their performance is limited and provides a warning that the design practices may be insufficient. The numerical simulation correlated well with the experimental response in terms of displacement capacity, strength, and hysteric behavior.

Seismic behavior of precast segmental bridge columns reinforced with hybrid FRP-steel bars

Precast segmental bridge columns (PSBCs) are a key component in accelerated bridge construction. In order to advance the technology and improve their seismic resistance, this paper presents research on an innovative PSBC system that incorporates both fiber-reinforced polymer (FRP) bars and steel bars as longitudinal reinforcement. The system, which is referred to as an FRP-steel reinforced PSBC (FSR-PSBC), utilizes hybrid FRP-steel bars to increase the post-yield stiffness and to decrease the post-earthquake residual drift. The first part of the paper presents the results of cyclic loading tests of large-scale PSBC systems. Several important trends were observed. (1) Compared to traditional steel-reinforced PSBCs, the post-yield stiffness ratio of the FSR-PSBC system increased by up to 93%, while the residual drift ratio reduced by 68% at a large drift of 4%. (2) The FSR-PSBC specimens exhibited energy dissipation capacities comparable to their steel-reinforced counterparts. (3) Carbon FRP bars of the hybrid reinforcement significantly contributed to the increase of the post-yield stiffness and self-centering ability of the FSR-PSBC system. The second part of the paper presents a design-oriented analysis of the test results. Three possible compression-bending failure modes of the FSR-PSBC system are proposed and a desired ductile failure mode was established. Then, three damage limit states within the ductile failure process were defined in terms of the responses of materials, displacement and residual drift. The analysis presented paves the way for the development of a performance-based seismic design method for an FSR-PSBC system.

Steel A-braced frame upgrade performance under various load characteristics

This study evaluated innovated A-braced frame design performance under cyclic load and twelve far-field and near-field earthquake ground motions. The proposed A-brace design combined pre-deformed brace segments, steel curved damper and lever mechanism to amplify steel curved damper deformation for effective energy dissipation. A series of cyclic loading tests on steel moment resisting frames with the proposed A-braces were conducted first. The cyclic load test results showed that A-braced frames exhibited higher stiffness than the moment resisting frame in both elastic and inelastic stages to effectively reduce the structural deformation. Significant strength and energy dissipation enhancements were achieved in A-braced frames, with maximum gains reaching 2.31 and 1.94 times, respectively, above those of the moment resisting frame. Seismic performance evaluation on multi-story framed structures revealed that lower structural base shear, reduction in story drift, approximately 30.86%, 27.61% and 27.51% for the 10, 6 and 3-story frames, respectively, and plastic hinge development elimination to prevent structural failure were achieved simultaneously when the A-brace was adopted. The A-braced frame performance enhancements under cyclic load and various earthquake ground motions effectively justified proposed method applicability to seismic structural design.

High-rise modular buildings with innovative precast concrete shear walls as a lateral force resisting system

Modular construction has been widely adopted for low-to-medium-rise buildings, but fairly limited for high-rises. A particular knowledge gap resides with the lateral force resistance of modular high-rises. Most such buildings adopt cast-in-situ cores for lateral force resisting, which is still labor-intensive. This paper aims to develop a new lateral force resisting system using precast shear walls as part of the modules for high-rises. A 40-story public housing building in Hong Kong was used for case study. A finite element (FE) model was developed to simulate the structural performance of the precast concrete shear walls and validated using results of cyclic loading tests. Using the FE model nonlinear static and dynamic analyses were conducted to examine the feasibility of the proposed system under the wind and seismic loadings in relevant codes. Multi-modal analysis further investigates the effects of higher modes on the seismic responses of the building. Results show that the developed FE model is effective to reproduce the structural performance of the precast concrete shear walls, and the proposed system is strong enough to resist wind and seismic loadings. Higher modes have considerable even dominant effects on seismic responses of the building. Using the cumulative contribution of modes to seismic demands is found appropriate to help select modes to calculate the seismic demands of high-rise modular buildings with the proposed lateral force resisting system.

Experimental Investigation of the Inelastic Response of Pig and Rat Skin Under Uniaxial Cyclic Mechanical Loading

Skin is a highly non-linear, anisotropic, rate dependent inelastic, and nearly incompressible material which exhibits substantial hysteresis even under very slow (quasistatic) loading conditions. In this paper, a series of uniaxial cyclic loading tests of porcine and rat skin at different strain rates and with samples oriented in different directions (with respect to the spine) were conducted to study the effect of strain rate and samples orientations with respect to spine on mullins effect and skin inelastic response. A noteworthy feature of skin is that, similar to certain filled rubbers, its mechanical response shifts after the first extension and exhibits softening and hysteresis when loaded under cyclic tension and mullins effect is observed. The results of these strain-controlled cyclic loading tests also indicated that the extent of softening is different for different strain rates and orientations. Also a substantial hysteresis persists even at very low strain rates indicating inelastic behavior beyond the rate sensitive viscoelastic response. Through this series of experiments, by investigating the effect of strain rate on pig skin and rat skin, we conclude that the skin response is rate dependent but inelastic and shows irreversible changes in fiber orientation which are observed in histology results. Also, skin shows persistent deformation that is only partially recovered even after a long period of unloading.

Seismic performance evaluation of reinforced concrete beam-column joints of existing buildings

Common computer programs generally model beam-column joint (BCJ) as a finite point without physical property that will neither yield nor fail. However, this assumption is not appropriate for modelling existing buildings without seismic provisions where the shear capacities of BCJs were uncertain. This paper presented the finite element analysis and cyclic load test results of four full-scale edge column BCJ specimens with and without column and BCJ shear link detailing according to seismic provisions. The aim was to compare the numerical analysis and experimental results to establish a reduction factor between BCJ with and without seismic detailing provisions and to verify the accuracy of numerical analysis results. With the proposed reduction factor, non-seismic provisioned BCJ that will fail under seismic actions can be determined from general computer analysis programs and correspondingly strengthened if necessary to ensure that yielding occurs in structural members connected to the joint instead of brittle joint shear failure. Furthermore, splitting crack along the lower column axis was observed in all non-seismic provisioned specimens due to eccentricity between the upper and lower column load centre and inadequate link confinement in the lower column.

Seismic Performance of Masonry Walls Built with New Type of Fired Shale Hollow Blocks

This paper presents the cyclic loading test results of a new type of fired shale hollow block masonry walls. Six specimens were designed including two specimens without reinforcements (bare walls) and four specimens constrained by structural columns (reinforced walls). The influences of aspect ratio, vertical compressive stress, and structural column on the seismic performance of the specimens were investigated. The failure mode, bearing capacity, ductility, stiffness degradation, and energy dissipation of specimens were analyzed. The results showed that the crack patterns of specimens changed from the horizontal straight shape (bare walls) to “X” shape (reinforced walls), and the corresponding bearing capacity, ductility, stiffness degradation, and energy dissipation of the specimens were improved. With the increase of the vertical compressive stress, the ductility and the secant stiffness of the specimens increased. Moreover, with the decrease of aspect ratio, the bearing capacity and secant stiffness of the masonry walls increased, while the energy dissipation capacity decreased. This paper confirms that fired shale hollow block walls could meet the seismic requirements through appropriate design, which could promote the application of this new type of block in civil engineering.

Earthquake-induced flow liquefaction in fines-containing sands under initial shear stress by lab tests and its implication in case histories

Volume change of sands in shearing is either contractive or dilative depending on relative positions to SSL (Steady State Line) on the void ratio versus effective stress state diagram. This strongly affects how sands tend to liquefy during earthquakes and behave thereafter under initial shear stresses loaded by sloping ground or nearby structures. Torsional simple shear undrained cyclic loading test results are addressed here to categorize liquefaction behavior of sand specimens with various relative densities and fines contents Fc so that the specimens are positioned on both sides of SSL under the effect of different initial shear stress. A flow-type failure on the contractive side of SSL is particularly focused, and how to evaluate its potential in terms of Fc under initial shear stress is discussed. Lastly, unprecedented liquefaction-induced flow failures recently occurred in very gentle slopes are addressed to discuss their basic mechanism and possible scenario in view of the findings in the laboratory tests.

Investigation on seismic performance and shear strength of high‐strength concrete‐filled polyvinyl chloride tube short columns

SummaryThis paper innovatively designs polyvinyl chloride tube (PVCT) with high‐strength concrete (HC) and presents the results of cyclic loading tests on new reinforced high‐strength concrete short columns, including three high‐strength concrete‐filled PVCT (HC‐PVCT) short columns, one high‐strength concrete‐filled steel tube short column and one HC short column. The main objective of this research was to evaluate the seismic behaviors of HC short columns based on the quasistatic test of the columns. The design parameters of the columns in the experiments were axial compression ratio, reinforcement measures, concrete strength, stirrups configuration, and the height‐diameter ratio of tubes. The crack distribution, failure modes, hysteresis loops, skeleton curves, energy dissipation capacity, strength degradation, stiffness degradation, and cumulative damage of the columns were presented and analyzed. The results showed that the HC‐PVCT column had a fuller hysteretic loop and a higher peak load than the HC column. Compared with HC column, the strength degradation of HC‐PVCT columns was slower, and the ductility increased significantly. With a larger axial compression ratio, the ductility of HC‐PVCT columns was decreased. Based on the test and analysis results, a modified HC‐PVCT design method was proposed to calculate the nominal shear strength of HC‐PVCT short columns.

Seismic behavior of normal-strength concrete-filled precast high-strength concrete centrifugal tube columns

This study reports the cyclic loading test results of normal-strength concrete-filled precast high-strength concrete centrifugal tube columns. Seven half-scale column specimens were tested under cyclic loads and axial compression loads to investigate their seismic behavior. The major parameters considered in the test included axial compression ratio, filled concrete strength, and volumetric stirrup ratio. The structural behavior of each specimen was investigated in terms of failure modes, hysteresis behavior, bearing capacity, dissipated energy, ductility, stiffness degradation, drift capacity, and strain profiles. Test results revealed that the concrete-filled precast high-strength concrete centrifugal tube column exhibited good integral behavior, and the failure modes of all columns were ductile flexural failures. Lower axial compression ratio and higher volumetric stirrup ratio resulted in more satisfactory ductile performance. In contrast, the filled concrete strength has a limited influence on the structural behavior of concrete-filled precast high-strength concrete centrifugal tube columns. Based on the limit analysis method, the calculation formula for the bending capacity of the concrete-filled precast high-strength concrete centrifugal tube column was developed, and the results predicted from the formulas were in good agreement with the experiment results.