Constant Axial Compressive Force Research Articles

Flexural behavior of curved steel-plate composite (SC) walls under combined axial compression and cyclic lateral force

The curved steel-plate composite (SC) walls, commonly used in nuclear power plants have not been adequately investigated. This paper aims at the curvature effects on the in-plane and out-of-plane flexural behavior of SC walls with consideration of axial compression. Eight specimens were tested under combined constant axial compression force and cyclic lateral force. The failure modes, moment-drift responses, ductility, stiffness degradation, ductility and energy dissipation are reported. Finite element (FE) models using ABAQUS were established and benchmarked with test results. Results show that the curvature effect on the structural behavior of curved SC wall is insignificant. For the flexural capacities of curved SC walls with T/R ratios no more than 0.5, negligible influential factors λ due to the curvature effect are seen. For the SC walls subjected to in-plane loading, −6.9% ≤ λIP ≤ 0.0% and when under out-of-plane loading, −6.9% ≤ λOP ≤ 6.0%. The plastic in-plane and out-of-plane flexural capacities of flat SC walls considering the axial compression were derived. To modify the proposed equations and determine their limitations, a parametric study was carried out in terms of the parameters including material grades of steel and concrete, reinforcement ratios, axial compression ratios.

Efficient application of the Reduced Stress Method for built-up I sections

Reduced Stress Method is an alternative to the effective width method of EN 1993-1-1. Because of its built-in conservatism it is less used in practice for the design of building structures. The proposed new application reduces this conservatism. The final stress distribution is obtained with a 2-step iteration which automatically handles the effect of the displacement of the center of gravity of the original gross cross-section. Instead of calculating effective widths or reducing the whole cross-section resistance, reduced thicknesses are assigned to the proper individual plates. Reduction is obtained using the standard plate buckling curves where the plate slenderness is calculated with the help of linear buckling analysis. The buckling shape relevant to each plates of the cross-section is selected with a deformation energy-based buckling sensitivity analysis. The proposed method is demonstrated on a series of welded I beam-column Class 4 sections subjected to constant axial compression force and strong axis bending moment. Resistances are compared with results obtained by the EN 1993-1-3 effective width method and by numerical simulation. The method is ready to be built into computer software which can handle shell finite elements and perform linear buckling analysis.

Lateral cyclic testing and backbone curve development of high-strength steel built-up box columns under axial compression

The AISC 341 (2016) has a more stringent width-to-thickness (b/t) limit for highly ductile hollow box columns (HBCs) than the AIJ (2010) or Taiwan Code (2010), resulting in significant thickness difference in design. Moreover, the cyclic backbone curves based on ASCE 41 (2013) and NIST (2017) underestimate the post-buckling flexural strength of HBCs, particularly in high axial compression force. This paper presents test results of six full-scale, built-up HBCs using SM 570 M steel with the actual yield strength of 460–530 MPa. The lateral cyclic behavior of built-up columns was studied in terms of different b/t ratios, magnitudes of axial compression forces, and lateral drift histories (i.e., cyclically symmetric versus near-fault displacement histories). The built-up box columns were 290–400 mm wide with b/t ratios from 11 to 21, 4000 mm high, and tested laterally with both ends fixed after under a constant axial compression force, 2591–7935 kN. The HBC specimens which were designed based on the highly ductile member requirement in AISC 341 (2016), even under an axial compression force (=40%Py), performed satisfactorily at 4% drift and experienced flange and web fracture at 5% drift. However, the HBC specimens that satisfied the most compact b/t requirement in AIJ (2010) or Taiwan code (2010) did not perform well at 4% drift, losing the axial capacity after significant column local buckling and shortening. The gathered test data, supported by more test data in this work, were analyzed by a multiple regression method to obtain empirical formulations for predicting the maximum column moment, plastic rotation and post-yield hardening parameters. The proposed formulation reasonably predicts the first-cycle envelope curves of built-up HBCs, improving prediction results based on ASCE 41 (2013) and NIST (2017).

Seismic evaluation of precast bridge columns with built-in elastomeric pads

A novel built-in elastomeric pad was incorporated into the plastic hinge zone of precast bridge columns with grouted corrugated duct connection to improve its seismic performance. Appropriate energy dissipation and minimal local concrete damage are expected in the innovative precast reinforced concrete (RC) columns. Four 1/4-scaled bridge column specimens were designed and tested under constant axial compression force and cyclic lateral loads to evaluate the feasibility and effectiveness of the proposed concept. Detailed experiment results were compared and discussed. The testing results showed that the main seismic index of precast RC bridge columns with grouted metal corrugated duct connection was similar to that of the cast-in-place bridge columns. It was also found that the precast RC column with a built-in elastomeric pad in the plastic hinge zone effectively minimized local concrete damage at the bottom of bridge columns and increased the energy dissipation capacity. The laminated elastomeric pad is recommended to be applied in the precast bridge column to maintain necessary initial stiffness and energy dissipation capacity and to avoid lateral bulge of single thick rubber. Excessive buckling and shear deformations of longitudinal rebars should be prevented by inserting a rectangular or square steel tube at the center of the elastomeric pad.

EFFECTS OF THE INITIAL DEFLECTION SHAPE ON THE MOMENT AMPLIFICATION FACTOR OF BEAM-COLUMNS

In the design of slender steel beam-columns, the moment amplification factor is used to estimate the maximum moment along with the longitudinal direction. While formulas for evaluating the factor have been presented on the basis of elastic or elastic-plastic analysis, the initial deflection of the column is not considered. The effect that the initial deflection on the strength and behavior of the column has been shown only when the initial deflection shape is half sine wave. This paper discusses the effect of the initial deflection shape on the value of the moment amplification factor by performing the analytical work. The analytical model is the hinged-end beam-column subjected to constant axial compressive force and end moments. First of all, the equilibrium differential equation which governs the problem is solved and the formula for calculating the bending moment is presented. In the parametric study, magnitude of initial deflection, initial deflection shape, axial load ratio, slenderness ratio and end moment ratio are selected as the parameters. In this paper, we discuss the effects of the amount of the initial deflection and the initial deflection shape.

Experimental and numerical investigation on the performance of three-legged CFST latticed columns under lateral cyclic loadings

To evaluate the cyclic performance of composite latticed columns, experiments and numerical modelling of three-legged concrete filled steel tube (CFST) latticed columns under constant axial compressive force and lateral cyclic loadings were conducted. Experiments of eight specimens, including 6 CFST latticed columns and 2 steel latticed columns, were carried out with various axial compression ratio and diameter-to-thickness ratio of the tube section in the limb. The failure pattern, hysteretic behaviour, bearing capacity, initial stiffness and accumulated energy dissipation of the specimens were investigated. The experimental results reveal that, under cyclic loadings, CFST latticed columns have better performance than the corresponding steel latticed columns; however, three-legged CFST latticed specimens show different behaviour in two loading directions owing to the different capacity of the CFST members under tension and compression. A finite element analysis (FEA) model was developed to simulate the performance of three-legged CFST latticed columns under lateral cyclic loadings, and the feasibility of the FEA model was verified by the comparison against test results.

Experimental study on seismic behaviour of an innovative composite shear wall

To improve the strength and ductility of the core walls in high-rise buildings which would be subjected to combined high axial compressive force and bending moment during the earthquake, an innovative concrete filled double-skin steel-plate composite (CFDSC) wall is proposed. The CFDSC wall is composed of the concrete filled double-skin steel-plate wall body with transverse stiffeners, vertical diaphragms and distributed batten plates welding on the internal surface of the double steel plates, and the concrete filled steel tube (CFST) columns including a pair of CFST columns positioned at the end of the cross section as boundary elements and an additional one located in the central section of the wall. Five CFDSC wall specimens were tested under constant axial compressive force and lateral reversed cyclic loading to investigate the seismic behaviour of the wall considering the effect of axial force ratio and shear span ratio. The favourable seismic performance of the CFDSC walls was demonstrated in the test. No serious pinching effect was observed on the hysteresis curves of all the specimens. The drift ratios corresponding to the ultimate stage were recorded as being in the range from 1/67 to 1/30 and the ductility coefficients were varied from 4.50 to 8.22. The experimental results manifest that the CFDSC walls have great energy dissipation capacity. Formulae for calculating the lateral load-carrying capacity of the CFDSC wall, taking the confinement effects from steel plates into account, were proposed. The results calculated by the proposed method show good agreement with the experimental results.

Seismic behavior of composite shear walls incorporating concrete-filled steel and FRP tubes as boundary elements

A new form of a composite shear wall consisting of a reinforced concrete (RC) wall web and two boundary columns, in the form of square concrete-filled steel tubes (CFST) incorporating a carbon fiber–reinforced polymer (CFRP)–confined concrete core, is proposed in this study. To evaluate its seismic performance, the proposed shear wall was tested under constant axial compression force and lateral cyclic loading. Three additional shear walls with different boundary column configurations were also tested: (i) an ordinary shear wall, (ii) a shear wall with CFST boundary columns, and (iii) a shear wall with double-skin CFST boundary columns. The failure mode, load-bearing capacity, ductility, energy dissipation capacity, stiffness degradation, strength degradation, and deformation mode of the four shear walls were thoroughly examined and compared. The results show that the deformation of the proposed shear wall was dominated by bending and that the distribution of axial strain generally satisfied the plane section assumption. The results also show that the seismic performance of the proposed shear wall was superior to that of the ordinary shear wall and the shear wall with CFST boundary columns. The proposed shear wall had the similar load-bearing capacity as the shear wall with double-skin CFST columns, but it had better ductility and larger dissipation capacity. This pilot study demonstrates that the composite shear wall has good potential for improving the performance of buildings constructed in seismic regions.

Behaviour and Failure of Steel Columns Subjected to Blast Loads: Numerical Study and Analytical Approach

The main objective of this study is the numerical simulation of the behaviour and failure patterns of steel columns under blast loads using the dynamic finite element package ABAQUS/Explicit. A numerical model is suggested and validated against published experimental tests on full-scale wide-flange steel columns subjected to dynamic blast loads under constant axial compressive force. Afterwards, the validated model is used to investigate the effect of important parameters on the behaviour and failure patterns of steel columns under blast pressure through an extensive parametric study. The parameters include the blast impulse, the blast energy, the blast load, the blast duration, the column boundary condition, the column slenderness ratio, and the blast direction. The conclusions extracted from this parametric study may be used to develop a thorough understanding of the behaviour and failure of steel columns subjected to blast load which, in turn, could lead to a more accurate practical design procedure. The study also presents derivations and validations of a proposed analytical approach to calculate the critical blast impulse at which a steel column losses its global stability. Comparison between the critical impulse-axial force curves obtained from the proposed equation and that extracted from numerical simulations indicates the validity and feasibility of the proposed equation.

MOMENT AMPLIFICATION FACTOR OF BEAM-COLUMNS WITH INITIAL DEFLECTION

In the design of slender steel beam-columns, the moment amplification factor is used to estimate the maximum bending moment. The formulas for evaluating the factor have been presented on the basis of the elastic or elastic-plastic analysis, however the initial deflection of beam-columns is not considered. This paper discusses the effect of initial deflection on the value of the moment amplification factor by performing the analytical work. The analytical model is a simply supported beam-column subjected to constant axial compressive force and end moments. First of all, the equilibrium differential equation which governs the problem is solved and the formula for calculating the bending moment is obtained. In the parametric study, magnitude of the initial deflection, the axial load ratio, the slenderness ratio and the end moment ratio are selected as the parameters. The effects of magnitude of the initial deflection and the end moment ratio on the moment amplification factor are discussed.

ULTIMATE STRENGTH OF CONCRETE FILLED SQUARE STEEL TUBULAR BEAM-COLUMNS

The objective of this study is to examine the ultimate strength of CFT columns. The range of the axial load ratio and the slenderness ratio in which CFT beam-columns reach the full plastic moment are examined on the basis of the strength formulas specified by AIJ Recommendation for Limit State Design of Steel Structures. The CFT columns are subjected to the constant axial compressive force and the monotonic moment at the one end, as the analytical parameters the axial load ratio and slenderness ratio are selected. The analysis is carried out by the shooting method. Bending moment-rotational angle relationships are calculated by the shooting method and the maximum strengths of CFT columns are obtained. When the value obtained by multiplying the axial load ratio and the second power of the slenderness ratio is 0.05, the maximum strength reach 95% of the full plastic moment under the condition that the axial load ratio value is less than or equal to 0.75. When the value obtained by multiplying the axial load ratio and the second power of the slenderness ratio is 0.1, the maximum strength reach 95% of the full plastic moment under the condition that the axial load ratio value is less than or equal to 0.5.

Experimental studies on behaviour of tubular T-joints reinforced with grouted sleeve

Tubular joints have been widely used in offshore platforms and space structures due to their merits such as easy fabrication, aesthetic appearance and better static strength. For existing tubular joints, a grouted sleeve reinforced method was proposed in this paper. Experimental tests on five tubular T-joints reinforced with the grouted sleeve and two conventional tubular T-joints were conducted to investigate their mechanical behaviour. A constant axial compressive force was applied to the chord end to simulate the compressive state of the chord member during the tests. Then an axial compressive force was applied to the top end of the brace member until the collapse of the joint specimens occurred. The parameters investigated herein were the grout thickness, the sleeve length coefficient and the sleeve construction method. The failure mode, ultimate load, initial stiffness and deformability of these joint specimens were discussed. It was found that: (1) The grouted sleeve could change the failure mode of tubular T-joints. (2) The grouted sleeve was observed to provide strength enhancement up to 154.3%~172.7% for the corresponding un-reinforced joint. (3) The initial stiffness and deformability were also greatly improved by the grouted sleeve. (4) The sleeve length coefficient was a key parameter for the improved effect of the grouted sleeve reinforced method.

Modal analysis of prestressed draft pad of freight wagons using finite element method

The present work intends to investigate dynamic behaviour of draft gear using finite element method. The longitudinal force that the draft gear absorbs usually leads to the failure of its components, especially, the load bearing draft pads. Dynamic behaviour of an individual draft pad and a draft gear is determined and characterized with exciting frequencies and corresponding mode shapes. The effect of compressive prestress load on the dynamic behaviour of an individual draft pad is also determined as the draft pads in assembled state are under constant axial compressive force in the draft gear. The vibration characteristics of individual draft pad are compared with draft pads that are part of draft gear. The modal analysis gives us a basis for subjecting a draft pad to higher frequency loading for determining its fatigue behaviour.

An In Vitro Model of Degenerative Lumbar Spondylolisthesis

A biomechanical human cadaveric study. To create a biomechanical model of low-grade degenerative lumbar spondylolisthesis (DLS), defined by anterior listhesis, for future testing of spinal instrumentation. Current spinal implants are used to treat a multitude of conditions that range from herniated discs to degenerative diseases. The optimal stiffness of these instrumentation systems for each specific spinal condition is unknown. Ex vivo models representing degenerative spinal conditions are scarce in the literature. A model of DLS for implant testing will enhance our understanding of implant-spine behavior for specific populations of patients. Four incremental surgical destabilizations were performed on 8 lumbar functional spinal units. The facet complex and intervertebral disc were targeted to represent the tissue changes associated with DLS. After each destabilization, the specimen was tested with: (1) applied shear force (-50 to 250 N) with a constant axial compression force (300 N) and (2) applied pure moments in flexion-extension, lateral bending and axial rotation (±5 Nm). Relative motion between the 2 vertebrae was tracked with a motion capture system. The effect of specimen condition on intervertebral motion was assessed for shear and flexibility testing. Shear translation increased, specimen stiffness decreased and range of motion increased with specimen destabilization (P < 0.0002). A mean anterior translation of 3.1 mm (SD 1.1 mm) was achieved only after destabilization of both the facet complex and disc. Of the 5 specimen conditions, 3 were required to achieve grade 1 DLS: (1) intact, (3) a 4-mm facet gap, and (5) a combined nucleus and annulus injury. Destabilization of both the facet complex and disc was required to achieve anterior listhesis of 3.1 mm consistent with a grade 1 DLS under an applied shear force of 250 N. Sufficient listhesis was measured without radical specimen resection. Important anatomical structures for supporting spinal instrumentation were preserved such that this model can be used in future to characterize behavior of novel instrumentation prior to clinical trials.

Experimental Study of CFRP Confined RC Rectangular Hollow Section Bridge Piers

To investigate the seismic performance of FRP strengthened RC hollow section bridge piers under multi-dimensional earthquake excitation, the pseudo-static test was carried out to RC rectangular hollow section as-built and CFRP confined bridge piers under constant axial compression force and bidirectional horizontal repeated load. The failure characteristics, lateral force-deformation curves and ductility of specimens were analyzed. The experimental result shows that CFRP constraining may change the failure mode of hollow section bridge piers, and significantly improve the deformation ductility, plastic deformation, however, it is less contribution to horizontal force of specimens with less wall-thickness.

Occurrence of strain nonuniformity in thin‐walled cylinders subjected to constant axial compressive force and cyclic torsion

Hysteretic behaviour numerical analysis has been carried out for elastic–plastic thin‐walled cylinders subjected to a constant axial compressive force and cyclic torsion. It is shown that various deformation modes appear, which are different from those under constant axial contraction, and that those modes cause rapid growth of strain nonuniformity. Also branching analysis for the same model has been performed according to symmetry limit theory and the predicted multiple branching behaviour is compared with the hysteretic behaviour.

Analysis of equal leg single-angle section beams subjected to biaxial bending and constant axial compressive force

Single-angle section beams are generally loaded parallel to their geometrical axes and their cross-sections are not symmetrical to their principal axes. Even equal leg angle beams have only one symmetrical axis. Many types of loading cause biaxial bending and axial forces in these members. Since single-angle section beams are slender members, they also need to be analyzed in terms of flexural buckling, lateral torsional buckling and local buckling effects. In this study, a calculation procedure is presented to analyze the nominal loads of equal leg angle section beams loaded vertically to the axis of the beam. It is assumed that the axial force is composed of a constant compressive force. The constant axial force is only taken into consideration for the uniform compressive stress and the second-degree effects caused in the cross-section. Thus only the biaxial bending moments remain. The first yield, full plastic and critical lateral torsional buckling moments for biaxial bending are calculated with respect to the slenderness of the beam and the axial force. The nominal design force on the cross-section is calculated according to the load and resistance factor design rules. The analysis proposed for the constant axial load can also be used for other axial forces, by using an iterative calculation procedure.

Seismic Performance of Square Reinforced Concrete Columns under Combined Cyclic Flexural and Torsional Loadings

This article presents an experimental investigation on the behavior of reinforced concrete cantilevered columns subjected to combined cyclic bending and torsional loading. Seven columnar specimens with the same structural properties were tested under various loading conditions: cyclic torsion, cyclic uniaxial bending, and combined cyclic torsion and cyclic uniaxial bending with and without a constant axial compression force. Several combinations of cyclic bending and cyclic torsion expressed in terms of the rotation–drift ratio r were applied to study the interaction between torsion and flexural capacity of columns. The result reveals that the flexural capacity decreases and the damage tends to occur upward outside the flexural plastic hinge region as the level of applied cyclic torsion increases. An empirical model for the flexural and torsional hysteretic behavior is proposed based on the experimental result.

The dynamic behaviour of elastic steel columns

The free vibrations of pin-ended steel columns in the elastic range are analysed by direct minimisation of an energy function. The columns are subjected to either constant axial compressive force, or constant axial shortening, and the (lateral) amplitude of vibration is prescribed. The analysis includes lateral deflections of magnitude comparable to the cross-section depth, and so is non-linear. The columns can either be initially straight, or can have an initial sinusoidal geometric imperfection of magnitude Δ0. The analysis is rapid, and is shown to give accurate results for the classical linear vibration problem. Results for initially imperfect columns demonstrate the significant effect of the manner in which the axial load is applied.