Behavior Of Structural Members Research Articles

Behavior of structural members under oblique impact loads state‑of‑the‑art review

Behavior of structural members under oblique impact loads state‑of‑the‑art review

Curing–dependent structural behavior of ultra-high-performance hybrid fiber-reinforced concrete beams

The application of ultra-high-performance fiber-reinforced concrete (UHP-FRC) is exceptionally versatile. However, a comprehensive understanding of UHP-FRC beam structural performance characteristics is lacking. The majority of research has concentrated on the behavior of structural members following standard water curing. This study investigated the impact of the curing regime on the structural performance of UHPC beams. The four different curing regimes used were standard, simulated hot arid weather, steam curing at various ages, and 5% sodium sulfate curing. Experimentally measured mechanical properties of UHP-FRC have been determined following ASTM guidelines, and the investigated beams have been tested under displacement-controlled four-point loading. Additionally, ACI 318 and FHWA-HIF codified formulas were employed in this study to predict the moment capacity of the tested beams. As a result of the various steam systems of varying ages, the load-carrying capacities of the beams were improved. By accelerating cement hydration, steam curing produces a stronger bond between fibers and the cementitious matrix, improving flexural strength. The control beam (under standard curing) showed a smaller maximum deflection, while all other beams showed similar deflection capacity. By accelerating the drying shrinkage, the beams under the 28-day standard with hot air curing were negatively impacted, with an average deflection value around 5% lower than control beams. The cured beams under simulated hot, arid conditions had the lowest flexural rigidity. A steam-cured beam had the highest moment-curvature performance, while a beam cured under simulated arid conditions had the lowest. Additionally, the ACI 318 design equation significantly underestimated beam maximum moments, while the FHWA approach marginally overestimated beam maximum moments with a predicted-to-tested average of 0.82.

Experimental and Analytical Studies of an Ultra-high Performance Concrete Beam Using Carbon Fiber Reinforced Polymer Bars

Infrastructure degradation attributable to concrete deterioration and corrosion of reinforcing steel has been a long-standing challenge to the owners and engineers. This problem becomes more evident when concrete structures are subject to aggressively corrosive environments. The use of advanced materials such as ultra-high performance concrete (UHPC) and carbon fiber reinforced polymer (CFRP) bars has a strong potential to overcome this challenge and help build new infrastructure that is durable and sustainable. However, structural behavior of members using both UHPC and CFRP bars has not been studied thoroughly in the United States and overseas, and no codes or specifications are readily available for structural engineers to follow. This paper presented an initial attempt to explore this topic by addressing the bond behavior between UHPC and CFRP bars through pullout tests. The test results showed that the UHPC specimens exhibited gradually increased slippage after the peak load and demonstrated superior bond performance in comparison with the conventional concrete specimens. Flexural tests were also conducted to compare the structural behavior of two large-scale beams, which were made of conventional concrete reinforced by steel bars and UHPC reinforced by CFRP bars, respectively. Test results showed that the UHPC beam did not exhibit as much ductility as the conventional beam, as predicted. However, there was still sufficient warning of impending failure in a form of extensive cracking and substantial deflection attributable to the bridging effect of the steel fibers. Further, flexural strength analysis of the UHPC beam using CFRP bars was discussed satisfying strain compatibility and force equilibrium, which provided a guidance for structural engineers to design such members. The research approach adopted in this paper may be applicable to study UHPC beams using other types of FRP materials.

Analytical Study on the Effect of Steel Fiber in the Deflection of Pre-Stressed Concrete Beams

Fiber reinforced concrete (FRC) is being widely used as the structural material owing to its superior engineering properties. From the past, it was understood that Fiber Reinforced Concrete had been proved to be well performing over the time under different practical situations. Fibers enhance the mechanical properties of concrete and in turn change the structbehaviouravior. It is observed that high strength fibers are available such as steel fibers, carbon fibers, basalt fibers, glass fibers etc. Large number of literatures are available to study the influence of these fibers on the flexural behavior of conventional concrete. Application of finite element analysis (FEA) in the behaviour of structural members is gaining momentum. The results from Finite Element Analysis need to be validated with the IS code provisions. In the present research work, an attempt was made to understand the effect of fiber in the deflection of Prestressed concrete beams both through Finite Element Analysis and Indian and American Codes.

Influences of the unsymmetrical bending on behaviour of structural members with a restrained lateral deflection

As reinforced concrete (RC) walls with different principal bending axes are connected by the floor diaphragms, unsymmetrical bending is frequently expected for structural members in resisting the lateral loads. In these cases, a portion of lateral reaction forces is anticipated to be perpendicular to the lateral deflection of the members which causes shear deformation and additional curvature perpendicular to the loading plane. This paper investigates these out-of-plane deformations and curvatures and their influences. Magnitude of these shear deformations and curvatures are investigated with experimental data and a theoretical solution. The results confirm that the out-of-plane curvature is related with disproportional shear and flexural stiffness of the wall in different principal bending directions and can account for a significant portion of the in-plane curvature. The curvature could introduce significantly higher strain and render the member more vulnerable to out-of-plane buckling. Methods for modelling the curvature in structural system are proposed based on nonlinear fibre element model.

Bond Characteristics of a Deformed Steel Bar Embedded in Donut-Type Voided Slab

In reinforced concrete (RC) structures, bond behavior between concrete and deformed steel bar (rebar) has a great effect on the structural behavior of members including voided slabs. According to previous research, bond behavior of a rebar in voided slabs is different from that in general RC slabs by the concrete inner cover formed between rebar and void. However, the bond characteristics of rebar in voided slabs have not been clearly verified yet. This study investigated the bond characteristics of rebar in the donut-type voided slab. Like other voided slabs, the donut-type void-shaper make concrete inner cover formed between rebar and void, and some part of the donut-type voided slab has smaller inner cover thickness than 2.5 db. Furthermore, inner cover thickness changes along the longitudinal rebar due to the shape of void. These were expected to affect the bond behavior of rebar in the donut-type voided slab. In this study, pull-out tests were performed to find out the effect of bond condition by the region due to voids. To this end, the donut-type voided slab was divided into three regions according to the shape of void, such as ‘Insufficient region’, ‘Transition region’, and ‘Sufficient region’. Main variables were inner cover thickness, embedded length, and bond location, which is affected by void shape. Bond characteristics of rebar in the donut-type voided slab were evaluated through comparison of bond stress–slip relationship, maximum bond strength, and bond stress distribution of each region. Test results showed that the average bond stress was found to be 25~50% lower than that of the general RC slab in the region of the inner cover thickness of 2.5 db, which was not satisfied due to void, and the bond stress–slip relationship and the bond stress distribution of the donut-type voided slab was also different from that of the general RC slab according to the type of bond region and inner cover thickness. In addition, the calculation method of bond strength of rebar in donut-type voided slab was proposed, which indicated that the error range between the estimated value and the experimental value was within 5%.

Mathematical Prediction on the strength and behaviour of structural member by incorporating Incinerated Bio-Medical Waste Ash in Ground Granulated Blast Furnace Slag based Geopolymer Concrete

Concrete seems to be the more commonly used construction substance throughout the entire globe as well as its usage have been expanded over the last decade because the demand for building works has increased. Geopolymer concrete (GPC) is one of the technologies that may be used to replace traditional concrete. Geopolymer concrete is an inorganic alumino-silicate polymer made mostly of silicon, aluminum, and by-product materials such as Fly Ash (FA), Ground Granulated Blast Slag (GGBS), and other by-product materials. While the key motives for utilizing GPC is technical and economic advantages, the avoidance of environmental pollution by appropriate waste management has become a concern. The primary goal of this research is to see how Incinerated Bio-Medical Waste Ash (IBWA) affects the mechanical and flexural activity of GPC. In this report, IBWA is substituted for GGBS in various percentages (0, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, and 50%). The inclusion of IBWA converts the substance from brittle to ductile, resulting in substantial improvements in tensile stress, tensile strain, toughness, and energy absorption capacities. The samples was held constant at ambient temperature throughout the curing phase. On concrete specimens, the mechanical properties of concrete, including the compressive strength of the cube, the split tensile strength and the bending strength were inspected. The experimental findings indicate that introducing IBWA to GPC enhances the mechanical behaviour of the material as well as the load carrying capability of the beams.

Comparative study on behavior of reinforced concrete columns with high Strength concrete and normal strength concrete

The usage of High strength concrete (HSC) concrete has predominantly increased over last few decades, compared to Normal strength concrete (NSC). But it is known that characteristic behavior of HSC and NSC are different as there difference in their stress strain behavior. So the behavior of structural member with HSC and NSC may differ. In this paper eccentric compressive behavior (Axial, Moment capacities) of reinforced concrete for both HSC and NSC are compared. Experimental work has been done to obtain stress strain curves for HSC (M60,M70) and NSC (M20,M30) using compressometer. The developed stress strain curves are used for development Axial-Moment interaction curves for HSC and NSC at various percent of reinforcements (1%,1.5%,2%,2.5%,3%,3.5%). The percentage of increase in axial, moment capacities of section with increase in percentage of steel for HSC and NSC at various d’/D values (0.05, 0.10, 0.15, 0.20) are compared and discussed.

Collapse performance of composite steel frames under fire

Collapse of steel structures under extreme hazards has been placed at the forefront of research in recent decades. While significant number of studies has been conducted in the past on steel members and subassemblies under fire, the response of steel buildings exposed to fire loadings has not received a similar level of attention. In addition, only handful of previous studies, mainly 2D with only one study pertaining to 3D frames, encompassed the full response of the system up to and including collapse. In this study, a 3D numerical finite element model is developed for a six-story steel-frame building with moment frames, gravity frames, and center concentrically braced frame to evaluate the collapse behavior of the structure under fire loading. A standard and a parametric fire curve are selected to simulate the fire loadings and are applied independently to the building model under two different contained fire scenarios. The two scenarios include first floor corner compartment fire and whole first floor fire. This allowed for the assessment of different global system response where collapse is triggered by twist of the entire structure accompanied by lateral deformation in the case of a corner compartment fire and progressive vertical displacement of the entire system in the case of the whole first floor fire. The simulation results show that structural response of steel buildings including collapse mechanism and behavior of structural members and connections during fire events can be predicted with reasonable accuracy using advanced numerical finite element analysis.

English

The reinforced concrete with fiber reinforced polymer (FRP) bars (carbon, aramid, basalt and glass) is used in places where a high ratio of strength to weight is required and corrosion is not acceptable. Behavior of structural members using (FRP) bars is hard to be modeled using traditional methods because of the high non-linearity relationship among factors influencing the strength of structural members. Back-propagation neural network is a very effective method for modeling such complicated relationships. In this paper, back-propagation neural network is used for modeling the flexural behavior of beams reinforced with (FRP) bars. 101 samples of beams reinforced with fiber bars were collected from literatures. Five important factors are taken in consideration for predicting the strength of beams. Two models of Multilayer Perceptron (MLP) are created, first with single-hidden layer and the second with two-hidden layers. The two-hidden layer model showed better accuracy ratio than the single-hidden layer model. Parametric study has been done for two-hidden layer model only. Equations are derived to be used instead of the model and the importance of input factors is determined. Results showed that the neural network is successful in modeling the behavior of concrete beams reinforced with different types of (FRP) bars.

Undergraduate laboratory exercise on impact testing of structures

This note reports on simple equations that can be used to interpret the behaviour of structural members struck by impact loads as used in a simple undergraduate laboratory exercise. The application of these equations is illustrated for some test results on a long vertical thin-walled top-hat section struck axially by a large mass at one end and supported on a rigid foundation at the other end. This is a particularly simple experimental arrangement, which is suitable for illustrating various features of the mass impact loading of a structural member to undergraduates. It is possible to predict various characteristics of the structural response with the aid of these equations and the minimum of instrumentation.

Part 4 Special Behaviors of Structural Members

Part 4 Special Behaviors of Structural Members

The influence of triggers geometry upon the stiffness of cylindrical thin walled tubes

AbstractToday’s automobile manufacturers are increasingly using lightweight materials to reduce weight; these include plastics, composites, aluminium, magnesium alloys, and also new types of high strength steels. Many of these materials have limited strength or ductility, therefore in many cases the rupture being serious consequences during crashes, underscore Picketta et al. in their studies.Automotive structures must deform plastically in a short period of time, a few milliseconds, to absorb the crash energy in a controllable manner. It must be light and enable economically mass-production [1].FE models rapidly gained acceptance among engineers. Many other factors facilitated the development of vehicle models by shell finite elements since most of the geometry of the structural surfaces was already on computer graphic files.Kee Poong Kim and Hoon Huh emphasize that the crashworthiness of each vehicle part needs to be evaluated at the initial stage of design for good performance of an assembled vehicle. As the dynamic behaviour of structural members is different from the static one, the crashworthiness of the vehicle structures has to be assessed by impact analysis.The paper analyzes the influence of trigger geometry upon the compression of thin-walled cylindrical tubes. Simulations performed on a simple model showed the dependence between triggers area and deformation times as well as the maximum deformations obtained for various speeds at which the simulations ware carried out. Likewise, the geometry of trigger leads to different results.

Investigation of Correlations between Seismic Parameters and Damage Indices for Earthquakes of Iran Region

Seismic record of an earthquake contains important and significant data about characteristics of a ground motion. In this study, interdependencies between important seismic parameters and three overall structural damage indices including the Bracci index, the modified flexural damage ratio (MFDR) index and the drift index were determined for several records of earthquakes occurred in Iran. Calculations were done for medium rise concrete frame structures. In next step, seismic parameters that had strongest and weakest interdependencies with three mentioned damage indices were determined by the Spearman and Pearson correlation coefficients. As the final value of damage indices cannot show the process of member degradation, time variations in the Powell and Allahabadi model were calculated to give a good insight into the behavior of structural members during earthquake.

Actual Effects of Local Buckling of Thin-Walled Metal Roof Decking: Control Experimental Verification Performed during Structure Realization

Experimental verification of structural members can be the necessary part of the structural design of load-carrying civil structures, mainly in the period of last two decades. In some cases, the knowledge obtained from the tests is the sole source of the reliable information about actual behaviour of structural member in strain and failure process and about its objective load-carrying capacity. The paper is specifically aimed at the control experimental verification of roof decking based on thin-walled metal profiled sheets. Loading test has been performed during structure erection, as additional resource for the verification of actual behaviour and objective load-carrying capacity and for the confirmation or refinement of static design assumptions and results, within the ultimate and serviceability limit states. The subject of the control experimental verification was roof decking composed of thin-walled metal cassettes with thermal insulation at its upper side, used for the university lecture room roofing.

933 周期材料からなる構造部材のツースケール時間依存変形解析(OS9,OS10 合同ポスターセッション,OS・一般セッション講演)

933 周期材料からなる構造部材のツースケール時間依存変形解析(OS9,OS10 合同ポスターセッション,OS・一般セッション講演)

Algorithm and Program for Simulating Heat Transfer in Cavities of Structural Members under Fire Conditions

In this paper, an algorithm based on the network method suggested by Oppenheim for calculating the radiative heat flow in a cavity of structural members, say hollow core concrete slabs, exposed to fires is presented. It is assumed that the pressure in a cavity keeps atmospheric pressure through the whole cause of a fire, and the lost heat from the air due to expansion and immediate moving away from a cavity is neglected. The heat in a cavity is transfer via both heat conduction in air and thermal radiation among boundaries, and special regard is paid to modeling heat transfer by radiation. The effective radiative heat flow system of equations is derived and expressed in matrix form. The system of equations features a symmetric coefficient matrix, which can be stored in a one dimensional array, and can be solved using LDLT factorization. Node radiative thermal loads are calculated from effective radiative heat flows at edges of elements located on internal cavities. The nonlinear finite element program TFIELD written by first author has employed the new algorithm. Temperature distribution in two structural members with cavities are calculated using TFIELD, and numerical results demonstrate that the new algorithm is very effective and is useful for further study of structural behavior of structural members under fire conditions.

The fatigue process of concrete and its structural influence

Fatigue of concrete is a microcracking process leading to the change of the macroscopic material properties. In particular, progressive stiffness decrease and increase of total and residual strains are developed as a function of the number of cycles and the stress level. The influence of the fatigue process on the behaviour of structural members is complex, because a cyclic redistribution of stresses develops within the structure. Owing to this fact, the employ of S-N curves to estimate the fatigue life usually leads to extremely conservative results. In this paper, a fatigue model for concrete is presented accounting for the evolution of the material properties. The model is able to obtain the fatigue life and the evolution of stresses and strains. The results are compared with other available design rules and a modification is proposed to estimate the number of cycles to failure in a simple way for the engineering practice.

Mechanical behavior of ferritic grade 3Cr12 stainless steel—Part 1: Experimental investigations

Ferritic stainless steels are corrosion resistant steels with a low and stable cost. Widely used in automotive applications, structural applications using ferritic stainless steels are only emerging mainly because ferritics are partially covered by structural standards due to a shortage of design data. Computer models are more and more used to support the developments of conventional design methods based on expensive full-scale tests or trial and errors methods. And for the modeling of metal forming processes as well as structural behavior of members, it is necessary to afford an accurate knowledge of the mechanical properties. In this paper, the experimental investigations made on the chromium based alloy 3Cr12 (1.4003) in order to characterize its mechanical behavior are presented. During the research, a classical uniaxial experimental equipment and a bi-axial experimental equipment designed by Flores (2005) [1] in the Structures Laboratory of the University of Liege have been used. The collection of tests performed included tensile tests, cyclic shear tests, simple shear tests and successive simple shear and plane-strain tests. The yield locus and the hardening models are presented and identified in a companion paper by the same author.

Fracture Characteristics for Crack Tip near the Interface between Steel and Concrete in Composite Structures

Steel-concrete composite structures are widely used in high buildings for its excellent seismic behaviors, whereas faults or cracks, which have great influence on interfacial mechanical behaviors of structural members, inevitably form near the interface between steel and concrete during the process of molding. Therefore, it is necessary to study the mechanical characteristics of the crack tip near the interface. In this paper, the application scope of the path-independence of J-integral in steel-concrete composite structure with a crack is discussed. According to the conservation law of J-integral for the steel-concrete composite structure with a crack parallel to the interface, a hypothesis that the value of strain energy release rate (SERR) of the mode-I fracture is independent of the crack location when the crack is parallel and close to the interface is put forwarded. And this hypothesis is verified through finite element method (FEM). A schematic model for a skew crack near the steel-concrete interface is provided. The variation law of SERR with the Dundur’s parameters and the angle between crack direction and interface are calculated by FEM. At last, calculating method of the stress intensity factor as well as the SERR for a skew crack near the interface is suggested. All these may contribute to further investigation on interfacial mechanical behaviors for steel-concrete composite structure.