Bidirectional Loading Research Articles

Development of a Minimal-Disturbance Rehabilitation System for Sustaining Bidirectional Loading

AbstractA light-weight and rapid seismic rehabilitation technique, named biaxial minimal-disturbance arm damper (biMDAD), is developed to upgrade steel buildings that are weak for seismically-induc...

Seismic testing of post-tensioned Pres-Lam core walls using cross laminated timber

With the increasing demand for multi-storey timber buildings in areas with high wind loads and high seismic activity, stiff lateral load resisting systems are becoming a crucial design component. Post-tensioned Pres-Lam mass timber lift shafts and stairwell core walls not only provide a strong and very stiff lateral load resisting system, but also damage limiting response in the case of a large seismic event.This paper describes the results of experimental tests on Cross-Laminated Timber (CLT) Pres-Lam core walls tested under bi-directional quasi-static seismic loading. In the first configuration the CLT wall panels were connected in the corners with screws, while in the second configuration, steel pivotal columns were introduced at the corners and the CLT wall panels were connected to the steel columns with dissipative U-shaped Flexural Plates (UFPs).Overall the testing showed that the Pres-Lam system, when used for structural timber core walls subjected to bidirectional loading regimes, sustains nominal damage after large drift demands. By adding ductile screw-connections or steel columns with UFPs at the corners additional strength and dissipation capacity is obtained.Friction between the CLT panels improved the seismic performance of the structure, which in Serviceability Limit State (SLS) conditions led to rigid behaviour of the splices between the panels. Displacement incompatibilities between the floor diaphragm and the core walls were accommodated by locating the connections at the centre of the walls, or by pinned connections in the corner pivotal columns. Relative displacements between orthogonally running connector beams were accommodated by using flexible connections out-of-plane. Under low axial forces there was horizontal sliding of the walls at the foundation level, but this was not observed when larger post-tensioning forces were applied.

Buckling analysis of orthotropic thin rectangular plates subjected to nonlinear in-plane distributed loads using generalized differential quadrature method

ABSTRACTIn the present work, buckling analysis of orthotropic thin rectangular plates with uniform thickness resting on Pasternak foundation are investigated for eight types of boundary conditions: SSSS, CCCC, SCSC, SSSC, SSCC, CCCF, SSFC, and CFCF. Based on classical plate theory, governing differential equation in buckling are solved numerically using generalized differential quadrature method (GDQM) to obtain critical buckling loads and corresponding modes. The kinds of nonlinear loading are presented in six cases including symmetrical and unsymmetrical distribution. In addition, the effects of aspect ratio, orthotropic moduli ratio and coefficients of foundation on the buckling load are illustrated. The present work is the first attempt to consider the influence of the nonlinearity of distributed in-plane bi-directional loading in determination of buckling load and representation of the corresponding shape modes. Some numerical examples are provided to demonstrate good accuracy of the GDQ method to evaluate the critical buckling load in case of nonlinear distributed bi-directional compressive loads. As shown, profile of distributed in-plane loading plays an important role on buckling behavior of the rectangular plate.

A pulsed Coandă-effect reciprocating wind energy generator

A radically new concept in small-scale wind-energy generation is presented that produces reciprocating motion of a bluff-body by periodically activating boundary layer control via blowing slots. The reciprocating motion is best suited to directly perform mechanical work, such as the pumping of liquids. A proof-of-concept scale-model technology demonstrator was constructed and tested. It consisted of a vertically-mounted circular cylinder, connected to a pivot at its lower end. The cylinder was counterbalanced by tension springs and useful mechanical loading was simulated by means of a calibrated electromagnetic brake. The cylinder included two diametrically disposed span-wise blowing slots that were pulsed alternately to produce bi-directional transverse loads (lift) made possible by the Coandă effect. Measurements included the static loads generated by the Coandă effect and system power performance evaluations. The former were used, together with a theoretical linear model, for performance predictions. Direct system performance measurements demonstrated a positive net power output, while model predictions indicated efficiencies of approximately 20%. Although the performance in terms of system efficiency, at this stage, is inferior to that of small wind turbines, several improvements were proposed in order to render the concept more energetically competitive.

Cyclic Behavior of Panel Zone in Steel Moment Frame under Bidirectional Loading

This paper aims to examine the cyclic behavior of panels in steel moment frame subjected to bidirectional and unidirectional loading and to demonstrate the differences of panel behavior under two loading modes. The specimens were composed of wide-flange beams and square tube columns, and the panel zones were designed to yield before columns and beams. Experimental results showed that specimens subjected to bidirectional loading suffered severe damage, caused by the weld fracture at the corner of panel-to-diaphragm weld, and failed at 0.06 rad and 0.04 rad story drift for specimens with panel aspect ratio of 1.4 and 2.0, respectively. Specimens subjected to unidirectional loading developed a story drift of 0.06 rad without strength reduction. The panels contributed about 60%-80% story drift and dissipated approximately 80% of total input energy. Panels with higher aspect ratio showed smaller plastic shear strength because of the effect of flexural yielding in panels. Moreover, the beams were found to present plastic moments 20%-50% lower than theoretical values, which was attributed to the small panel-to-beam strength ratio.

Steel Columns under Multi-Axis Seismic Loading: Experimental Findings and Design Recommendations

This paper summarizes the findings of two test programs that investigated the hysteretic behavior of wide-flange columns in steel moment-resisting frames. Both deep and shallow steel columns were examined. The members were subjected to unidirectional and bidirectional lateral loading histories coupled with constant and varying axial load demands. The experimental findings highlight the dependence of the steel column response on the member end boundary conditions, the biaxial bending, the loading history, as well as the test-scaling. Steel columns subjected to high axial load demands do not behave as force-controlled elements as suggested by current nonlinear modeling recommendations in North America. Accordingly, an updated axial force limit is proposed in this case. Moreover, in light of the test findings, seismic design recommendations are proposed to limit column damage during strong earthquake shaking.

Bidirectional Behaviour of Unstiffened and Stiffened Direct-Welded Connections for Square CFST Columns

This paper describes finite element analyses of two-way moment frame beam-column joint subassemblies constructed using steel I-shaped beams connected to square concrete filled steel tubular (CFST) columns. These are direct-welded connections with (i) no stiffeners, (ii) internal horizontal stiffener plates, (iii) vertical tube stiffeners, and (iv) the combination of (ii) and (iii). They were analyzed under one-way and two-way column lateral loading. It is shown that internal stiffeners increase the joint stiffness and strength by up to 80% and 60% respectively. The effect of bidirectional loading on the joint capacity is found to be minor. A design method is developed to predict the required stiffener capacity. The method is applicable for both one-way and two-way loading cases.

Сalibration method for a strain-gauge measurement system based on bidirectional rail loading

At present, all railways tend to increase the speed of passenger trains and axle loads in transportation of goods. These processes contribute to the improvement of rolling stocks and railway infrastructures. At the same time, there is a need to maintain a high level of safety in transportation. Therefore, experimental research and feasibility studies of the existing monitoring solutions are of the highest priority. Being experimental in nature, this study is aimed at increasing the reliability of the strain-gauge method in measurement of dynamic forces transferred from the wheel to the rail in real operating conditions. Rail strains were experimentally studied under bidirectional loading using a special-purpose impact device. Results of this research are presented in the paper. An experimental measuring section was created for recording loads. Strain gauges were installed on rails in several cross-sections. Rails were loaded with a special-purpose device, which was designed to adjust a loading force and shift a contact point. The structure of the loading device and its basic features are described in the paper.

Influence of Bidirectional Impact Loading on Anomalously Low‐Friction Effect in Block Rock Media

The anomalously low‐friction effect is a key scientific problem in deep mining. The deep coal rock media is usually a block structure with joint fracture. When the deep block coal rock is subjected to repeated strong dynamic impact caused by long‐term excavation activities, the anomalously low‐friction effect will occur, resulting in dynamic disasters such as rock bursts. Taking granite block rock media as research object and using bidirectional impact loading to simulate the dynamic disturbance of rock media, a numerical model was established. The vertical acceleration and the horizontal displacement on working block media were defined as the characteristic parameters of the anomalously low‐friction effect. The effects of delay time and horizontal impact loading amplitude and frequency on the characteristic parameters under bidirectional impact loading were examined by numerical simulation. The generation and variation of the anomalously low‐friction effect of block rock media subjected to bidirectional impact loading were presented. The results show that the delay time has a significant effect to the vertical acceleration amplitude and horizontal displacement on the working block media under bidirectional impact loading. There exists a delay time threshold; when reach to the threshold, quasiresonance and the anomalously low‐friction effect on block media will easily occur. With the increase in horizontal impact amplitude, the residual horizontal displacement on the working block media also increases by power function, while it decreases by power function with the increase of horizontal impact loading frequency. Finally, this study denotes that it is great significance to investigate the bidirectional impact loading in order to capture the mechanism of anomalously low‐friction effect.

Earthquake resistance of reinforced concrete corner beam-column joints with different column axial loads under bi-directional lateral loading

The seismic performance of a corner beam-column joint in reinforced concrete frames was studied by testing two three-dimensional corner beam-column subassemblage specimens without slabs under constant column axial load and bi-directional lateral cyclic load reversals. The column-to-beam flexural strength ratio was varied from 1.4 to 2.3 by changing the magnitude of column axial load. Although a sufficient margin to prevent shear failure was provided to a corner beam-column joint in the test, the subassemblage specimens failed in joint hinging after beam and column longitudinal bars and joint hoops yielded. The ultimate joint hinging capacity of a corner joint under bi-directional lateral loading was enhanced by an increase in column compressive axial load, and can be estimated based on the new mechanism proposed by Kusuhara and Shiohara.

Cyclic behavior of panel zone in beam-column subassemblies subjected to bidirectional loading

This paper aims to examine the cyclic behavior of panels in beam-column subassemblies subjected to bidirectional and unidirectional loading and to demonstrate the differences of panel behavior under two loading modes. The specimens were composed of wide-flange beams and square tube columns, and the panel zones were designed to yield before columns and beams. Experimental results showed that specimens subjected to bidirectional loading suffered severe damage, caused by the weld fracture at the corner of panel-to-diaphragm weld, and failed at 0.06rad and 0.04rad story drift for specimens with panel aspect ratio of 1.4 and 2.0, respectively. Specimens subjected to unidirectional loading developed a story drift of 0.06rad without strength reduction. The panels contributed about 60%–80% story drift and dissipated approximately 80% of total input energy. Elastic stiffness of panels correlated well with theoretical values that were considered both flexural and shear stiffness. Panels with higher aspect ratio showed smaller plastic shear strength. Finite element analysis indicates that the lower plastic shear strength was resulted from flexural yielding in panels, and the effect of flexural yielding became more considerable under bidirectional loading. Moreover, the beams were found to present plastic moments 20%–50% lower than the theoretical values, which was attributed to the small panel-to-beam strength ratio.

Numerical Study on Biaxial Seismic Performance of Reinforced Concrete Box Piers Based on OpenSees

In order to study the seismic performance of reinforced concrete box piers under biaxial loading, the hysteretic model of reinforced concrete box piers was established by selecting appropriate material model, constitutive relation, structural element type, and the corresponding boundary conditions and loading method based on OpenSees. The numerical simulation of the ductility of reinforced concrete box piers with different axial compression ratio, stirrup ratio and slenderness ratio under biaxial horizontal loading was conducted. The results of biaxial quasi-static tests and that of numerical simulation were compared. The analysis showed that the hysteretic behaviour of reinforced concrete box piers under biaxial loading could be well simulated and the degradation of strength and stiffness of box piers in the process of bidirectional cyclic loading could be reflected by OpenSees on the basis of the appropriate material constitutive model and structural element type. Furthermore, the influence of reinforcement ratio and concrete strength on the ductility of reinforced concrete box pier was studied by OpenSees.

Full-Scale Testing of Deep Wide-Flange Steel Columns under Multiaxis Cyclic Loading: Loading Sequence, Boundary Effects, and Lateral Stability Bracing Force Demands

This paper discusses the findings from 10 full-scale steel column tests subjected to multiaxis cyclic loading. The columns use deep wide-flange cross sections typically seen in steel moment-resisting frames designed in seismic regions. The effects of boundary conditions, loading sequence, local web, and member slenderness ratios on the column hysteretic behavior are investigated. The test data underscore the influence of boundary conditions on the damage progression of steel columns. Local buckling followed by out-of-plane deformations near the plastified column base are the dominant failure modes in fixed base columns with a realistic flexible top end. Twisting may occur only at drifts larger than 3% even when the member slenderness is fairly large. The test data suggest that bidirectional loading amplifies the out-of-plane deformations but does not significantly affect the overall column performance. The loading sequence strongly affects the column’s plastic deformation capacity but only at story drifts larger than 2%. Above this drift amplitude, column axial shortening grows exponentially and becomes a controlling failure mode. Measurements of the lateral stability bracing force demands at the column top exceed the lateral brace design force specified in North American standards.

Calcium signaling of in situ chondrocytes in articular cartilage under compressive loading: Roles of calcium sources and cell membrane ion channels.

Mechanical loading on articular cartilage can induce many physical and chemical stimuli on chondrocytes residing in the extracellular matrix (ECM). Intracellular calcium ([Ca2+ ]i ) signaling is among the earliest responses of chondrocytes to physical stimuli, but the [Ca2+ ]i signaling of in situ chondrocytes in loaded cartilage is not fully understood due to the technical challenges in [Ca2+ ]i imaging of chondrocytes in a deforming ECM. This study developed a novel bi-directional microscopy loading device that enables the record of transient [Ca2+ ]i responses of in situ chondrocytes in loaded cartilage. It was found that compressive loading significantly promoted [Ca2+ ]i signaling in chondrocytes with faster [Ca2+ ]i oscillations in comparison to the non-loaded cartilage. Seven [Ca2+ ]i signaling pathways were further investigated by treating the cartilage with antagonists prior to and/or during the loading. Removal of extracellular Ca2+ ions completely abolished the [Ca2+ ]i responses of in situ chondrocytes, suggesting the indispensable role of extracellular Ca2+ sources in initiating the [Ca2+ ]i signaling in chondrocytes. Depletion of intracellular Ca2+ stores, inhibition of PLC-IP3 pathway, and block of purinergic receptors on plasma membrane led to significant reduction in the responsive rate of cells. Three types of ion channels that are regulated by different physical signals, TRPV4 (osmotic and mechanical stress), T-type VGCCs (electrical potential), and mechanical sensitive ion channels (mechanical loading) all demonstrated critical roles in controlling the [Ca2+ ]i responses of in situ chondrocyte in the loaded cartilage. This study provided new knowledge about the [Ca2+ ]i signaling and mechanobiology of chondrocytes in its natural residing environment. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:730-738, 2018.

Experimental investigation of SRHSC columns under biaxial loading

The behavior of 8 steel reinforced high-strength concrete (SRHSC) columns, which comprised of four identical columns with cross-shaped steel and other four identical columns with square steel tube, was investigated experimentally under cyclic uniaxial and biaxial loading independently. The influence of steel configuration and loading path on the global behavior of SRHSC columns in terms of failure process, hysteretic characteristics, stiffness degradation and ductility were investigated and discussed, as well as stress level of the longitudinal and transverse reinforcing bars and steel. The research results indicate that with a same steel ratio deformation capacity of steel reinforced concrete columns with a square steel tube is better than the one with a cross-shaped steel. Loading path affects hysteretic characteristics of the specimens significantly. Under asymmetrical loading path, hysteretic characteristics of the specimens are also asymmetry. Compared with specimens under unidirectional loading, specimens subjected to bidirectional loading have poor carrying capacity, fast stiffness degradation, small yielding displacement, poor ductility and small ultimate failure drift. It also demonstrates that loading paths affect the deformation capacity or deformation performance significantly. Longitudinal reinforcement yielding occurs before the peak load is attained, while steel yielding occurs at the peak load. During later displacement loading, strain of longitudinal and transverse reinforcing bars and steel of specimens under biaxial loading increased faster than those of specimens subjected to unidirectional loading. Therefore, the bidirectional loading path has great influence on the seismic performance such as carrying capacity and deformation performance, which should be paid more attentions in structure design.

Interesting Developments in Testing Methods Applied to Foundation Piles

Both: piling technologies and pile testing methods are a subject of current development. New technologies, providing larger diameters or using in-situ materials, are very demanding in terms of providing proper quality of execution of works. That concerns the material quality and continuity which define the integral strength of pile. On the other side we have the capacity of the ground around the pile and its ability to carry the loads transferred by shaft and pile base. Inhomogeneous nature of soils and a relatively small amount of tested piles imposes very good understanding of small amount of results. In some special cases the capacity test itself form an important cost in the piling contract. This work presents a brief description of selected testing methods and authors remarks based on cooperation with Universities constantly developing new ideas. Paper presents some experience based remarks on integrity testing by means of low energy impact (low strain) and introduces selected (Polish) developments in the field of closed–end pipe piles testing based on bi-directional loading, similar to Osterberg idea, but without sacrificial hydraulic jack. Such test is suitable especially when steel piles are used for temporary support in the rivers, where constructing of conventional testing appliance with anchor piles or kentledge meets technical problems. According to the author’s experience, such tests were not yet used on the building site but they bring a real potential especially, when the displacement control can be provided from the river bank using surveying techniques.

Principal Stress Rotation under Bidirectional Simple Shear Loadings

Previous researches have indicated the non-coaxiality of sand in unidirectional simple shear tests, in which the direction of the principal axes of stresses does not coincide with the corresponding principal axes of strain rate tensors. Due to the limitation of apparatus that most of testing facilities can only add shear stress in one direction, the influence of stress history on the noncoaxiality of sand is not fully considered in previous tests. In this study, the effect of stress history on the non-coaxiality of sand is systematically studied by using the first commercially available Variable Direction Dynamic Cyclic Simple Shear system (VDDCSS). Samples of Leighton Buzzard sand (Fraction B) are first consolidated under a vertical confining stress and consolidation shear stress, and then sheared by a drained monotonic shear stress. Angle (θ) between the consolidation shear stress and the drained monotonic shear stress is varied from 0° to 180°, with an interval of 30°. The change of principal axes of stresses is predicted by well-established equations, and the principal axe of strain rate is calculated using recorded data. Results show that the level of non-coaxiality is increased by the increasing θ, especially at the initial stage of drained shearing.

11.29: Updates to the ASCE‐41‐13 provisions for the nonlinear modeling of steel wide‐flange columns for performance‐based earthquake engineering

ABSTRACTPerformance‐based earthquake engineering requires numerical models that are able to reliably predict the expected component behavior of buildings under seismic excitations. The nonlinear modeling guidelines provided in ASCE‐41‐13 have historically been used in this context by practicing engineers. However, for steel wide‐flange columns, the recommendations are primarily based on experimental data that was fairly limited until recently. This paper addresses many of the limitations present in ASCE‐41‐13 for the modeling of steel wide‐flange columns. Recent experimental data from large‐ and full‐scale tests on wide‐flange steel columns, supplemented with detailed finite element studies, has been collected for a wide range of column cross‐sections and applied compressive axial loads. Multiple regression analysis is utilized to develop multivariate predictive equations for the seismic response of steel wide‐flange columns. It is found that the primary contributors that dominate the column response are the local web slenderness, member slenderness and the applied axial load ratio due to gravity loading. Guidelines for developing nonlinear component models for steel columns that can be directly used in both nonlinear static and dynamic analysis procedures are provided. The predicted responses are validated against test data that was not part of the original database. Furthermore, recommendations are proposed for modeling wide‐flange columns subjected to varying axial loads as well as bidirectional loading; and a new limit for force‐controlled elements is proposed for columns under high axial compressive loading and lateral drift demands.

New bidirectional multilevel inverter topology with staircase cascading for symmetric and asymmetric structures

Inverters, as one of the key components of electrical systems, have experienced a great evolution in the last decade, and their performance improvement is a challenge even today, leading to many researches on topologies and control schemes. This study introduces a new multilevel converter topology which is able to supply bidirectional current loads. The proposed structure has fewer power electronic devices such as power switches, driver circuits, power diodes, and DC voltage sources and, can be designed in both symmetric and asymmetric structures. In order to increase the number of output levels and the proposed basic unit development, modular expansion or cascading methods can be used. This study demonstrates that the aforementioned methods have the best results in asymmetric and symmetric structures of the proposed topology, respectively. The comparison between the proposed converter and some previous topologies shows that it has better conditions with respect to the used semiconductor count, switching and conduction losses, and total blocking voltage. The operation and performance of the proposed multi-level converter have been ascertained through simulations and verified experimentally for a single-phase symmetric thirty-one-level inverter which shows the proposed converter's ability in smooth sinusoidal output voltage generation with minimum total harmonic distortion.

Shake Table Tests on Single-Story Dhajji Dewari Traditional Buildings

ABSTRACTThis article presents shake table tests carried out on two reduced scaled models, including 1/3rd scaled single room model and 1/4th scaled two rooms house model Dhajji Dewari (timber-braced frame rubble stone masonry) traditional structures for seismic performance evaluation. Multiple excitations tests were performed on the model structures using natural accelerograms with increasing intensity to deform the structure from elastic to inelastic and extreme damage state. The structure observed damage states, acceleration, and displacement response and lateral force-deformation behavior are retrieved. The tested structure models showed an excellent performance under the earthquake ground motions; deforming to large lateral displacement without jeopardizing the global stability despite extreme level shaking and observed localized damages. The model under bi-directional loading, reproduced through diagonal excitation, was observed with relatively reduced lateral strength and lateral deformation, due to walls subjected to both in-plane and out-of-plane loading. The research highlights the importance of dynamic excitation on the seismic performance evaluation of Dhajji structures. Analytical models are used for the capacity evaluation of considered Dhajji buildings, which shows promising performance in calculating the building yield stiffness and strength. Displacement-based method is used for the intensity-based seismic performance assessment of individual building in the highest seismic zone (PGA = 0.40 g, Soil Type D), which shows that Dhajji building under orthogonal loading will not exceed even the Immediate Occupancy level under design level earthquake ground motions. However, the building can just exceed the Life Safety level in design level ground motions, under diagonal excitation.