Results Of Monotonic Loading Tests Research Articles

Bolt-free post-tensioned connection for steel-framed modular buildings and design for optimal preloading

This paper introduces a novel bolt-free preloaded column-to-column connection, termed the ‘AJ connection’, for steel-framed modular buildings. The AJ connection is classified as a post-tensioned inter-module connection, and modules are connected vertically by preload, using specially designed couplers and high-tensile steel rod bolts (SRB) within the columns. The AJ connection enables easy assembly and disassembly processes of modular buildings by inducing preload on top of the modules using a torque or impact wrench, thus improving construction speed and reusability. The paper also establishes a design method, not previously attempted in the literature, to determine the minimum necessary preload for the connection. The primary aim of this method is to design against potential failures by gap-opening and slip between modules, commonly associated with existing post-tensioned inter-module connections. The effectiveness of the suggested method is verified through numerical simulations using FE joint models that have been calibrated against monotonic loading test results. Furthermore, the study investigates the adverse effects of gap-opening and slip at the connection on the performance of the beam-to-column joint and the SRBs within the columns. The findings indicate that (i) minimising the difference between the flexural stiffness of the floor and ceiling beams reduces the impact of gap-opening, and (ii) the rotation of the coupler caused by plate bearing due to slip prior to gap-opening affects the induced preload in the SRBs and leads to premature gap-opening at the connection.

Optimization of the Mechanical Properties of Bolted Connections between Concrete-Filled Tubular Columns and Steel Beam with Reinforcing Rings

To study the mechanical performance of bolted connections with different structural forms of reinforced rings, based on the results of monotonic loading tests on two bolted connections between a concrete-filled steel tubular column and a steel beam with an outer reinforcing ring, this article uses ABAQUS v.2020 software to establish a three-dimensional refined finite element analysis model of such connections using appropriate constitutive models for concrete and steel. Subsequently, the effect of the dimensions of the steel beam, reinforcing ring, and cover plate on the load-bearing properties and the failure mechanism of the connections is investigated, and the numerical model is consistent with the verification test results. Then, the numerical simulations comparing bolted exterior reinforced rings under seven different construction measures (i.e., number of bolts, stiffeners) based on a conventional welded exterior reinforced rings with rigid connections (i.e., CGJ) are standardized. The research results indicate that when four rows of bolts are introduced on exterior reinforced rings, the web of steel beam is welded with stiffeners, and the top and bottom reinforced rings are also added with stiffeners; this bolted connection with an external reinforcing ring (i.e., GZ-7) can achieve the rigidity and load-bearing capacity of a fully welded external reinforcing ring rigid connection. At the same time, the reinforcing ring plate is bolted to the flange of the steel beam, and the force transmission path at the connection is changed to avoid the brittle fracture easily caused by the welded flange joints. It is also in line with the development trend of sustainable construction of “assembly” and “disassembly”.

Behaviour of soilbags subjected to monotonic and cyclic vertical loading

Soilbags have been successfully used in the reinforcement of building foundations that can function as the base isolation. A series of unconfined compression tests under monotonic and cyclic loading were conducted to investigate the static bearing capacity and the dynamic deformation behaviour of stacked soilbags. The results of monotonic loading tests demonstrate that the ultimate compressive strength and the tangent compression modulus of soilbags tend to relatively stable values of around 0.7 MPa and 6.73 MPa, respectively, when the number of layers exceeds three. Under cyclic loading, the accumulated vertical strain of stacked soilbags increases nonlinearly under the application of cyclic loading, reducing with each loading cycle and even reaching a relatively stable state where the vertical strain is primarily elastic, which can be described with an empirical formula with respect to the static vertical stress, the cyclic load ratio and the number of loading cycles. The resilient moduli of stacked soilbags change slightly during cyclic loading period, and increase with the increasing static vertical stress and the decreasing cyclic load ratio. The outcomes of this study demonstrate the feasibility of soilbags as the base isolation as they have prominent bearing capacity and stable deformation behaviour under cyclic loading.

Monotonic and reverse-cyclic load experiment for plywood and RC slab diaphragms used in timber-concrete hybrid building

In seismically active regions, the use of timber-reinforced concrete (RC) hybrid construction can overcome the structural limitations that occur with timber construction. A series of shake table tests were carried out on RC-timber hybrid systems that used two diaphragms: glulam+plywood system (CN75 @ 50mm nail spacing) and laminated wood+RC slab system. To develop robust analytical models, however, understanding the different components is crucial. In this paper, a series of in-plane monotonic and reverse-cyclic tests were undertaken on two diaphragm systems and their connections. Salient features of each diaphragm (i.e. stiffness, ductility, and energy dissipation) were computed from the monotonic loading test results. With the test results reported, analytical and numerical models can be developed.

Connections for Timber–Concrete Hybrid Building: Experimental and Numerical Model Results

AbstractIn seismically active regions, the use of timber–reinforced concrete (RC) hybrid construction can overcome the structural limitations that occur with timber construction. This paper investigates three connections used in the timber frame–RC core hybrid system: (1) RC wall-timber beam connection, (2) timber column-base connection, and (3) timber beam-timber column connection. A series of monotonic and reverse-cyclic loading tests were conducted on three replicate connections. Salient features of each connection (i.e., stiffness, ductility, and energy dissipation) were computed from the monotonic loading test results and were used to set the backbone curve of the analytical Pinching4 hysteretic model. Furthermore, the Pinching4 hysteretic models were calibrated with the reverse-cyclic loading test results. Utility of the Pinching4 hysteretic models was shown with performance prediction of a portal frame test. The portal frame results showed good agreement between the finite element model using the c...

STUDY ON TORSION PROPERTIES OF CARBON FIBER SHEET STRENGTHENED PC MEMBER WITH ZEBRA-SHAPED

In this research, carbon fiber sheet (CFS) substitute to lateral tie was used for torsional strengthening of PC member. To investigate the mechanical properties of CFS strengthened PC member subjected to torsion and torsional reinforcement effects of CFS, monotonic and cyclic torsional loading tests were carried out with specimens which strengthened by lateral ties and unreinforced specimen for comparison. From both monotonic and cyclic loading test results, it was proved that the CFS can increase the ultimate torsional capacity and cracking torque. And it was also confirmed that the CFS had sufficient reinforcement effect, and for CFS strengthened specimen, the cracks of concrete were dispersed and widths were small. Mechanical properties such as torsional rigidity retention, residual twist, resilience and ductility were excellent. As for three-dimension finite element method analysis, analysis results matched the results of monotonic loading tests well and tracked the cyclic torsional loading tests when both nonlinear properties and hysteresis properties of each material were applied. A calculation concept including torsional effective cross-sectional area and thickness of shearing flow for the torsional capacity of CFS strengthened PC member was proposed.

STUDY ON TORSION PROPERTIES OF CARBON FIBER SHEET STRENGTHENED PC MEMBER WITH ZEBRA-SHAPED

In this research, carbon fiber sheet (CFS) substitute to lateral tie was used for torsional strengthening of PC member. To investigate the mechanical properties of CFS strengthened PC member subjected to torsion and torsional reinforcement effects of CFS, monotonic and cyclic torsional loading tests were carried out with specimens which strengthened by lateral ties and unreinforced specimen for comparison. From both monotonic and cyclic loading test results, it was proved that the CFS can increase the ultimate torsional capacity and cracking torque. And it was also confirmed that the CFS had sufficient reinforcement effect, and for CFS strengthened specimen, the cracks of concrete were dispersed and widths were small. Mechanical properties such as torsional rigidity retention, residual twist, resilience and ductility were excellent. As for three-dimension finite element method analysis, analysis results matched the results of monotonic loading tests well and tracked the cyclic torsional loading tests when both nonlinear properties and hysteresis properties of each material were applied. A calculation concept including torsional effective cross-sectional area and thickness of shearing flow for the torsional capacity of CFS strengthened PC member was proposed.

Response of Concrete to Dynamic Elevated-Amplitude Cyclic Tension

A universal testing machine was used to test the behavior of concrete subjected to cyclically varying load whose amplitude was constantly increasing. How concrete's dynamic strength has been affected by the rate of amplitude increment per loading cycle, cycle frequency, and initial static loading intensity has been studied. It was found that in concrete subjected to cyclically varying loading's strength enhancement, an important role was played by each cycle maximum loading rate in the frequency range of earthquake excitation. The amplitude increment rate's influence is insignificant. The authors present a formula for strength enhancement prediction of concrete which has been subjected to cyclically varying load based on monotonic loading test results. That concrete subjected to carrying cyclic loading's strength enhancement showed a tendency, with increasing initial static loading, to decrease, was revealed through experimental results. Unrecoverable plastic deformation magnifies along with loading cycle growth.

鉄骨骨組地震応答解析のための耐力劣化を伴う簡易部材モデル

In this papaer, inelastic portion of steel beam-columns are modeled as a simple mechanism composed of inelastic bars and a shear panel. A hysteresis rule for the bar behaviors is also proposed in consideration of strain-hardening, softening due to Bauschinger's effect, and resistance deterioration due to local buckling failure as well. The parameters of the model are calibrated to the results of monotonic loading tests on H-shaped and box-shaped members. Then the response analysis based on the model was performed and compared with the results of the on-line earthquake response tests. It was confirmed that their global responses were well predicted by the present model.