Presence Of Axial Load Research Articles

Study on hysteresis performance of corroded CHS T-joints under in-plane bending load

This research aims to examine the hysteresis behavior of corroded circular hollow section (CHS) T-joints when subjected to cyclic bending loading. Quasi-static tests including the coupling of brace axial load and in-plane cyclic moment were conducted on corroded CHS T-joint specimens to analyze the effects of corrosion damage on the hysteresis curve, failure mechanism, carrying capacity, and energy dissipation of the joints. Experimental results indicated the corrosion damage located at the different regions of joints had varying effects on the hysteresis behaviors of CHS T-joints. 1) The brace corrosion degree was more severe than the chord corrosion degree under the same exposure condition, however, the chord corrosion had a more significant influence on reducing the stiffness and ultimate carrying capacity of CHS T-joints. The ultimate capacity of CHS T-joints was found to decline by more than 20 % when the equivalent thickness loss of the chord was about 9.2 %. 2) Compared with chord corrosion, the brace corrosion would relieve the concave deformation and local plastic deformation of the chord so that more plastic cyclic damage concentrated around the intersection line. As a result, the through cracks prematurely occurred from the crown points on both sides, and the energy dissipation of CHS T-joints declined by more than 25 % when the equivalent thickness loss of the brace was about 13 %. The presence of axial loading on the brace not only affects the symmetry of hysteresis curves in CHS T-joints with non-uniform corrosion, but also exacerbates the concave deformation of the chord in chord corroded joints during the failure stage, thereby affecting the shape of hysteresis loops and fracture behavior of CHS T-joints when subjected to in-plane cyclic bending load.

Experimental study on exterior precast concrete beam-to-CECFST column joints with wet connections under cyclic loading

Concrete-encased concrete-filled steel tube (CECFST) structural system has gained popularity in recent years due to its several advantages over conventional structures. Additionally, precast technology has become an effective way of improving construction efficiency and environmental performance. Therefore, it is essential to investigate the structural behaviour of precast concrete (PC) beam-to-CECFST column joints to ensure their optimal performance in applications. In this regard, this paper presents an experimental study of 4 precast exterior joints subjected to lateral cyclic loading. The study investigated the effect of replacing normal concrete with steel fibre-reinforced concrete at the joint region and the presence of axial load on PC composite joints. Based on the test results, cyclic load-carrying resistance, failure modes and crack patterns of the PC specimens were recorded and analysed. In addition, a Digital Image Correlation (DIC) system was adopted to show the crack evolution of joint specimens and calculate shear strains of concrete encasement at the joint region. Further comparisons were conducted in terms of ductility, energy dissipation, stiffness and strength degradation to investigate the joint performance. Finally, existing American and European design code provisions were modified and used to predict joint shear strength. Their predictions were reasonably close to the test results.

Out-of-plane behavior of U-shaped unreinforced masonry structures

The out-of-plane behavior of masonry walls is an important aspect of their response, particularly in seismic regions. While previous studies have examined various geometries and materials, there exists a dearth of research on U-shaped walls, specifically with diverse geometric configurations. Moreover, the influence of axial load on out-of-plane behavior remains largely unexplored, limiting practical applications. This study aims to bridge these gaps by comprehensively investigating the out-of-plane behavior of U-shaped walls, focusing on the quantification of variable parameters encompassing geometry and axial load. A three-dimensional finite element model using the macro-modeling approach is used to analyze the structural response of U-shaped masonry walls under out-of-plane loading. The accuracy of the numerical modeling approach has been validated by available experimental test results to demonstrate the effectiveness of the modeling approach in predicting the out-of-plane behavior of U-shaped masonry structures. Subsequently, a series of parametric studies delves into the impacts of distinct geometrical attributes, including thickness, height, and span size, shedding light on the behavior of these walls across diverse geometric configurations. The results indicate that the capacity of the wall at the connection between out-of-plane and cross walls significantly influences the overall behavior and the failure mode. It was found that axial load substantially increases the strength of walls, in order of 1.5–3 times, and the positive effect of axial load was more significant than the secondary effects in most cases, though the significance of secondary effect drastically increases by increasing the height. It is shown that walls with longer span have much better behavior in the presence of axial load. Based on the results, for each specific geometrical parameter, a linear function can be considered for relation between strength and axial load. These findings can provide useful insights for the design and analysis of U-shaped masonry structures, particularly in seismic regions where out-of-plane behavior is a critical factor in their performance.

Axial-flexural strength of steel-concrete composite shear walls

A predictive equation is proposed for the axial-flexural strength of rectangular and flanged Composite Plate Shear Walls-Concrete Filled (C-PSW/CF), with and without endplates and boundary elements. The proposed equation is based on plastic stress distribution, adjusted by coefficients to account for influential design parameters. The adjustment coefficients are established by a regression analysis performed on the data developed using an extensive numerical parametric study. The continuum-based finite element model used for the simulations is first validated using the available test data. The effects of various design variables, including the aspect ratio, slenderness ratio, reinforcement ratio, axial load ratio, infill concrete compressive strength, and yielding strength of the steel faceplates on axial-moment are then numerically examined. Four cross-sections, including double skin plate, double skin plate with endplates, double skin plate with boundary elements, and double skin plate with flanges, are considered. The results are used to develop a new predictive equation to obtain the flexural strength of C-PSW/CFs in presence of axial loading. The proposed equation is finally validated using the experimental test data and its accuracy is evaluated by comparing it to available predictive equations and the method proposed by the 2016 AISC Seismic Provisions. The results show that the proposed design equation can well predict the flexural moment capacity of C-PSW/CFs with various cross-sections in presence of axial loading.

Nonlinear Response of RC Columns Subjected to Equal Energy-Double Impact Loads

Defining the damage and deflection from impact by using only the impact energy could be misleading due to the effect of impact momentum. In addition, reinforced concrete columns might be subjected to repeated impact loading. Hence, this study presents the numerical simulation of 16 RC columns with identical sizing and reinforcement details, subjected to equal energy-double impact loadings using a free-falling mass at midspan. The impact energy was kept constant for both impacts. For each analysis, the impact momentum was varied by varying the velocity and mass of the impactor. The axial load ratios of the columns are between 0.0 to 0.3 of the compressive strength of the concrete cross-section. The results clearly addressed the momentum effect on the impact responses. The momentum level affected the specimens’ damage behavior under the same input impact energy. A high momentum impact yielded more global flexural damage with large deflection, and a low momentum impact produced more local damage with a slight deflection. The axial load helps maintain the impact resistance capacity. However, the failure determined by the flexural damage pattern under the first impact was changed when subjected to the second impact to the shear mode with the presence of axial load. Further, the colliding index considering the momentum was used in the deflection prediction equation. The proposed equation improved the deflection calculation accuracy of reinforced concrete beams under equal energy but different momentum impact.

Experimental and numerical study of axially loaded reinforced concrete columns and frame columns under lateral impact loading

Pendulum impact tests were conducted on a reinforced concrete (RC) frame column and four RC free-standing columns. The effects of the axial compression ratio and reinforcement ratio on the impact resistance of the columns were compared using the dynamic time curves of framed and freestanding columns under impact. The test results show that for the same impact load, although the presence of axial loads can play a positive role (e.g., reducing the residual displacement), it may lead to more severe local damage. In addition, compared with free-standing columns, frame columns can be considered as a protective structure because of their greater lateral stiffness and stronger crashworthiness. The corresponding finite element models are developed, and the influence of the axial loads on the cross-section force responses under impact excitation was deeply explored. Axial loads can significantly affect the distribution of moment, shear force, and damage to the column.

Numerical study of hybrid GFRP-steel reinforced concrete shear walls and SFRC walls

Experimental results show that concrete shear walls reinforced with a hybrid scheme of steel and fiber-reinforced polymer (FRP) bars are able to achieve similar strength, stiffness and ductility to the walls constructed of conventional steel-reinforced concrete (RC). The elastic response of the FRP bars provides self-centering capacity to the system and mitigates the post-yield strength deterioration observed in the typical hysteretic response of RC walls, while the steel reinforcement provides ductility and energy dissipation capacity. Evidently, adoption of this innovative type of wall in construction requires a better understanding of performance of the hybrid system at the material and system levels, both through experimental testing and development of reliable numerical models. In this study, the finite-element analysis model developed by the authors is used to conduct a comprehensive parametric study on hybrid GFRP-steel reinforced shear walls. First, the validated model is used to address some other design aspects of tested specimens such as presence of axial load and arrangement of GFRP bars. Next, the reliability of the section analysis based on CSA A23.3-14 code for design of conventional and hybrid squat walls are investigated. The self-centering and economic aspects of design of hybrid GFRP-steel reinforced walls are also addressed. Using the analysis model, a promising structural application of SFRC (steel fiber-reinforced concrete) shear walls is also proposed. Findings of this study can assist practitioners with a more reliable and convenient shear wall design.

PHAETHON: Software for Analysis of Shear-Critical Reinforced Concrete Columns

Earthquake collapse of substandard reinforced concrete (RC) buildings, designed and constructed before the development of modern seismic design Codes, has triggered intense efforts by the scientific community for accurate assessment of this building stock. Most of the proposed procedures for the prediction of building strength and deformation indices were validated by assembling databases of RC column specimens tested under axial load and reversed cyclic lateral drift histories. Usually a column structural behavior is assessed by considering all involving mechanisms of behavior, namely flexure with or without the presence of axial load, shear and anchorage. In the present paper a force-based fiber beam/column element was developed accounting for shear and tension stiffening effects in order to provide an analytical test-bed for simulation of experimental cases such as the lightly reinforced columns forced to collapse. Their peculiar characteristics are the outcome of the shear – flexure interaction mechanism modeled here based on the Modified Compression Field Theory (MCFT) and the significant contribution of the tensile reinforcement pullout from its anchorage to the total column’s lateral drift. These features are embedded in this first-proposed stand-alone Windows program named “Phaethon” -with user’s interface written in C++ programming language code- aiming to facilitate engineers in executing analyses both for rectangular and circular substandard RC columns.

The influence of impact direction and axial loading on the bone fracture pattern

The effect of the direction of the impact and the presence of axial loading on fracture patterns have not yet been established in experimental 3-point bending studies. PurposeTo reveal the association between the direction of the force and the fracture pattern, with and without axial loading. Material and methodsA Dynatup Model POE 2000 (Instron Co.) low energy pendulum impact machine was utilized to apply impact loading on fresh pig femoral bones (n=50). The bone clamp shaft was adjusted to position the bone for three-point bending with and without additional bone compression. Four different directions of the force were applied: anterior, posterior, lateral, and medial. ResultsThe impacted aspect can be distinguished from the non-impacted aspects based on the fracture pattern alone (the most fractured one); the impact point can be identified on bare bones (the area from which all oblique lines radiate and/or the presence of a chip fragment). None of our experiments (with and without compression) yielded a “true” butterfly fracture, but instead, oblique radiating lines emerged from the point of impact (also known as “false” butterfly). Impacts on the lateral and anterior aspects of the bones produce more and longer fracture lines than impacts on the contralateral side; bones subjected to an impact with axial loading are significantly more comminuted and fragmented. Under axial loading, the number of fracture lines is independent of the impact direction. Our study presents an experimental model for fracture analysis and shows that the impact direction and the presence of axial loading during impact significantly affect the fracture pattern obtained.

Response of Pile Groups Driven in Sand Subjected to Combined Loads

Although the loads applied on piles are usually a combination of both vertical and lateral loads, very limited experimental research has been done on the response of pile groups subjected to combined loads. Due to pile–soil–pile interaction in pile groups, the response of a pile group may differ substantially from that of a single pile. This difference depends on soil state and pile spacing. This paper presents results of experiments designed to investigate pile interaction effects on the response of pile groups subjected to both axial and lateral loads. The experiments were load tests performed on model pile groups (2 × 2 pile groups) in calibration chamber sand samples. The model piles were driven into the sand samples prepared with different relative densities using a sand pluviator. The combined load tests were performed on the model pile groups subjected to different axial load levels, i.e., 0 (pure lateral loading), 25, 50, and 75% of the ultimate axial load capacity of the pile groups, defined as the load corresponding to a settlement of 10% of the model pile diameter. The combined load test results showed that the bending moment and lateral deflection at the head of the piles increased substantially for tests performed in the presence of axial loads, suggesting that the presence of axial loads on groups of piles driven in sand is detrimental to their lateral capacity.

Semi-analytical and numerical estimates of anchor losses in bistable MEMS

Anchor losses are one of the dominant sources of dissipation in micro-structures and their influence is even increased in the presence of axial loads. MEMS in which they are likely to play a major role include bistable elements which are nowadays commonly employed in shock sensors and energy harvesters. In this contribution we compute anchor losses both with a semi-analytical approach based on the theory of beams and a fully 3D finite element method including PML for wave dissipation. The two techniques provide coherent predictions and confirm the expectations of strong anchor losses. A fully analytical model is also proposed in the range of limited compressive forces and represents a valid tool for the design of new devices.

Accelerated corrosion investigation of axially loaded reinforced concrete elements

Purpose – This paper aims to present results of an experimental investigation on a series of scaled reinforced concrete column elements which were subjected to chloride exposure under accelerated conditions under a concurrent service axial load, over a period. In the presence of an axial load, directed microcracks of increasing density and width are introduced in the concrete mass, depending on the axial load level. Such cracks are believed to enhance the intrusion rate of chlorides in the concrete, relative to what is obtained in the normally performed unloaded specimen tests. Design/methodology/approach – Eighteen column specimens were tested over two chloride exposure periods, of duration up to a maximum of six months. Three different service axial load levels were considered, namely, none, 22 per cent and 43 per cent of the normalized axial load capacity of the columns. Findings – The results indicate that the specimens loaded to the higher axial load, which closely resembles actual service situation of such type of elements, exhibited up to ten times faster rates of induced current flow under a constant applied voltage of 500 mV, compared to the unloaded and less loaded specimens. Practical implications – It is proven that the presence of axial load influences the rate of chloride ingress in columns and, therefore, should be taken into account in estimating the concrete cover of such elements in durability design. Originality/value – The influence of axial loading on corrosion rate has not been considered in published experimental and analytical studies of chloride ingression. These studies have typically so far considered the accelerated corrosion of unloaded column specimens.

Buckling and lateral buckling interaction in thin-walled beam-column elements with mono-symmetric cross sections

Effects of axial forces on beam lateral buckling strength are investigated here in the case of elements with mono-symmetric cross sections. A unique compact closed-form is established for the interaction of lateral buckling moment with axial forces. This new equation is derived from a non-linear stability model. It includes first order bending distribution, load height level and effect of mono-symmetry terms (Wagner’s coefficient and shear point position). Compared to the so-called three-factors (C1–C3) formula commonly employed in beam lateral buckling stability, another factor C4 is added in presence of axial loads. Pre-buckling deflection effects are considered in the study and the case of doubly-symmetric cross sections is easily recovered. The proposed solutions are validated and compared to finite element simulations where 3D beam elements including warping are used. The agreement of the proposed solutions with bifurcations observed on the non-linear equilibrium paths is good. Dimensionless interaction curves are dressed for the beam lateral buckling strength and the applied axial load, where the flexural-torsional buckling axial force is a taken as reference.

Experimental Investigation of the Combined Load Response of Model Piles Driven in Sand

Abstract Although the load applied on a pile is usually a combination of a vertical and a lateral load, there have been few studies done on the response of piles subjected to combined loading; these studies; in addition, produce results that are inconsistent with respect to the effects of axial loads on the lateral load response of piles. In this paper, we present the results of model pile load tests performed to assess the influence of axial loads on the lateral response of piles driven in sand. Using a drop hammer, an instrumented circular model pile was driven into large-scale sand samples prepared in a cylindrical steel tank with various densities using a pluviation method. Lateral load tests were performed on the model pile subjected to different axial loads. The combined load test results showed that the presence of an axial load on a driven pile is detrimental to its lateral capacity, for the lateral deflection of the model pile head increased with increasing axial load. The bending moments at the pile head increased substantially (by 10 %, 36 % and 39 % for loose, medium dense and dense sand, respectively) in the presence of axial loads.

Post-fire cyclic behavior of reinforced concrete shear walls

The effects of fire exposure, reinforcement ratio and the presence of axial load under fire on the seismic behavior of reinforced concrete (RC) shear walls were investigated. Five RC shear walls were tested under low cyclic loading. Prior to the cyclic test, three specimens were exposed to fire and two of them were also subjected to a constant axial load. Test results indicate that the ultimate load of the specimen with lower reinforcement ratio is reduced by 15.8% after exposure to elevated temperatures. While the reductions in the energy dissipation and initial stiffness are 59.2% and 51.8%, respectively, which are much higher than those in the ultimate load. However, this deterioration can be slowed down by properly increasing reinforcement due to the strength and stiffness recovery of steel bars after cooling. In addition, the combined action of elevated temperatures and axial load results in more energy dissipation than the action of fire exposure alone.

A Generalized Constraint Model for Two-Dimensional Beam Flexures: Nonlinear Strain Energy Formulation

Abstract The beam constraint model (BCM), presented previously, captures pertinent nonlinearities to predict the constraint characteristics of a generalized beam flexure in terms of its stiffness and error motions. In this paper, a nonlinear strain energy formulation for the beam flexure, consistent with the transverse-direction load-displacement and axial-direction geometric constraint relations in the BCM, is presented. An explicit strain energy expression, in terms of beam end displacements, that accommodates generalized loading conditions, boundary conditions, initial curvature, and beam shape, is derived. Using energy-based arguments, new insight into the BCM is elucidated by fundamental relations among its stiffness, constraint, and energy coefficients. The presence of axial load in the geometric constraint and strain energy expressions—a unique attribute of distributed compliance flexures that leads to the elastokinematic effect—is highlighted. Using the principle of virtual work, this strain energy expression for a generalized beam is employed in determining the load-displacement relations, and therefore constraint characteristics, of a flexure mechanism comprising multiple beams. The benefit of this approach is evident in its mathematical efficiency and succinctness, which is to be expected with the use of energy methods. All analytical results are validated to a high degree of accuracy via nonlinear finite element analysis.

Shear Strength of Lightly Reinforced Wall Piers and Spandrels

Between the 1950s and 1970s, a significant number of buildings were constructed using lightly reinforced perimeter walls with openings. Evaluation and rehabilitation of such buildings requires accurate assessment of the expected shear strength, stiffness, and ductility of the wall segments (wall piers and spandrels) that comprise the primary lateral load-resisting elements. Assessing wall shear strength is complicated by factors such as use of a single curtain of distributed reinforcement, lack of hooks, and use of weakened plane joints, which are all common in older construction. To address these issues, a database of existing test results was assembled and reviewed; and tests were conducted on lightly reinforced wall piers and spandrels to address significant gaps in the available test data. Observations indicate that the amount of boundary reinforcement provided, presence of axial load, and the location of a weakened plane joint on the wall are the most important factors in the assessment of nominal shear strength.

Lateral buckling of thin-walled beam-column elements under combined axial and bending loads

Based on a non-linear stability model, analytical solutions are derived for simply supported beam-column elements with bi-symmetric I sections under combined bending and axial forces. An unique compact closed-form is used for some representative load cases needed in design. It includes first-order bending distribution, load height level, pre-buckling deflection effects and presence of axial loads. The proposed solutions are validated by recourse to non-linear FEM software where shell elements are used in mesh process. The agreement of the proposed solutions with bifurcations observed on non-linear equilibrium paths is good. It is proved that classical linear stability solutions underestimate the real resistance of such element in lateral buckling stability especially for I section with large flanges. Numerical study of incidence of axial forces on lateral buckling resistance of redundant beams is carried out. When axial displacements of a beam are prevented important tension axial forces are generated in the beam. This results in important reduction of displacements and for some sections, the beam behaviour becomes non-linear without any bifurcation.

Long-term flexural cracking of reinforced concrete members

A rational and simple analytical model to predict the time varying cracking moment of reinforced concrete sections under sustained loading is developed. The modeling procedure is based on equilibrium and compatibility requirements and takes into account the interdependent effects of creep and shrinkage as well as the presence of axial loading. A parametric study is conducted in which particular consideration is given to the effects of reinforcement ratio, level of loading, and creep and shrinkage characteristics of concrete. It is concluded that the reduction in cracking moment is mainly attributed to shrinkage. The effect of shrinkage is more pronounced at low levels of sustained loading and at high reinforcement ratios. This effect is lessened by the compression steel and creep particularly when the applied moment is near the cracking moment.

Behaviour of reinforced high-strength concrete beam—column joint. Part 1: experimental investigation

The beam–column joint is one of the important structural elements of reinforced concrete structures. It has been the subject of intensive research for the past four decades. To date, most of the design procedures of joints have been devoted to ordinary-strength concrete as implemented in the current international design codes. The use of high-strength concrete has become useful because of the advantages of member size limitation and higher structural capacity. However, its applicability is still limited because its behaviour, especially under combined stresses and shear, differs from ordinary-strength concrete in the presence of axial loading on the column. Consequently, the existing design guidelines are not completely applicable. In order to establish the salient features of the behaviour, namely modes of failure, deformational characteristics, strength parameters and strain development, an experimental programme was performed on beam–column joints under quasi-static monotonic loading. The influence of axial compression, along with other actions imposed on the joint including shear and bending moment, was taken into consideration. The practical aspects of using a composite structure—that is, ordinary-strength concrete of different grades at floor level and high-strength concrete along the rest of the column—were considered. The effects of different permutations of longitudinal as well as transverse reinforcement and various configurations of stirrups were also investigated.