Ultimate Resistance Research Articles

Bolted shear connectors in steel–concrete composite structures: Shear behavior

The use of bolted shear connectors is of great importance to the sustainable development of steel–concrete composite structures. In this paper, an experimental program consisting of four push-out specimens is performed to investigate the effects of bolt length and fabrication method of concrete slabs on the shear behavior of single-nut embedded bolted shear connectors in terms of failure mode and load-slip response. The concrete slabs are fabricated either as cast-in-situ monolithic slabs or precast slabs with reserved pockets which will be filled with grout in the final construction stage. The obtained results demonstrate that the fabrication method based on grouting, which is commonly utilized for strengthening and retrofitting works, does not affect the behavior of the bolted shear connection. Based on the experimental observations, a finite element (FE) model of the bolted shear connection is developed, after the obtained numerical results are verified against the test results obtained in this paper and those presented in other existing literature, a parametric study is carried out to further investigate the effects of the concrete strength, bolt strength, bolt diameter, bolt pretension load, and the length-to-diameter ratio of bolt on the performance of the bolted shear connection. Moreover, based on the obtained results, a design formula is proposed to obtain the ultimate shear resistance of the bolted shear connection, and the efficacy of the proposed design formula is proved through the comparison with the test results shown in the existing literature.

Shear Testing of Topologically Optimised Web Cover Plates in Splice Connections-Experiment Design and Results.

Testing shear-resisting plates in steel connections is one of the most challenging laboratory undertakings in steel construction, as the most common experimental layout design includes simulating the connection with its adjoining members. This significant hindrance gained particular magnitude as the need to test prototypes of topologically optimised shear cover plates became more pressing. Indeed, new code-compliant topology optimisation approaches for steel construction have recently been offered, and physically non-linear analyses have been demonstrated to be vital for assessing these elements. Hence, a rapid and reliable experimental process has become a fundamental necessity. To answer this need, a novel layout is herein proposed, in which topologically optimised and previously numerically examined bolted shear plates of a well-known steel joint were tested. The results allowed for the definition of the material trilinear model for use in subsequent numerical analysis, as well as the validation of the numerical simulation results. The discrepancy between the previously mathematically anticipated and empirically determined ultimate resistance did not exceed 1.7%.

Laterally loaded pile response in spatially variable soil

The spatial variability of soil has long been recognised, yet there is a dearth of research on the response of piles under lateral loading that considers this variability, especially for the lateral load transfer (P-y) curve in spatially variable clay. To address this gap, the study presents a three-dimensional random finite element analysis utilising a non-stationary random field to model soil variability with a linearly increasing trend. The results reveal that the spatial variability significantly affects the lateral capacity of the pile, emphasising the importance of accounting for this variability in pile design. Additionally, the study finds that while the spatial variability affects the failure mechanism, the mechanism remains comparable to that observed in deterministic analyses. The spatial variability has a substantial effect on ultimate soil resistance pressure, which can be fitted using a normal probability distribution function. An adjust factor is suggested to calculate the characteristic value, and from this characteristic value, the fractiles of ultimate soil resistance pressure can be calculated. This study provides an evaluation method for the spatial variability effect of soil, facilitating a cost-effective design of pile foundation.

Advanced finite element modelling of stainless steel bolted T-stubs under large deformations

Following upon the recently published experimental and numerical studies on stainless steel bolted T-stubs in tension, this study reports the development and validation of an advanced FE model that reveals the effect of initial contact between the bolts and bolt holes and constructional imperfections on the response of stainless steel bolted T-stubs subjected to large deformations. Key simulation strategies regarding the modelling of bolts, initial position of the bolts, flange bowing effect due to the initial constructional imperfections and overcoming numerical instabilities are discussed. The developed FE model first validated against the available test data in the literature. The effect of pre-established contact between the bolts and bolt holes and constructional imperfections on the overall response of the bolted T-stubs are reported comprehensively by comparing the plastic and ultimate resistances with the experimental ones. Moreover, the membrane action developing in the flange influences the ductility reserve of the T-stub which has a vital role in case of progressive collapse and robustness scenarios. Therefore, by inspecting the stress distribution through the flange thickness at various locations along the T-stubs, effects of different modelling configurations on the flexural and the membrane component of the load transfer mechanism are revealed. A parametric study is performed to investigate the influence of all these aspects on resistance of T-stub connections. On the basis of the obtained results and the discussions, modelling recommendations for the simulation of stainless steel T-stubs are made.

Anti-sliding performance of parallel wire strand clamps at elevated temperatures

This study investigated the influence of temperature on the anti-sliding performance of prestressed parallel wire strand clamps (PWSCs) through experiments and numerical analyses. The ultimate anti-sliding resistance of the clamps at different temperatures was obtained through steady-state experiments, and formulae for calculating high-temperature reduction factors of anti-sliding resistance were proposed. When the temperature reaches 400 °C, the ultimate anti-sliding resistance that the cable clamps can withstand is only 20.8% of the ambient temperature. The function between the ultimate fire resistance time of the PWSC and thrusting load level was proposed under ISO-834 heating conditions through transient-state experiments. It was found that the higher the thrusting load level, the shorter the fire resistance time that the PWSC can withstand. When the load level is 0.9Ffc,20, the fire resistance time of the specimen is only 38.1% of that under 0.3Ffc,20. The bolt pretension loss process of PWSCs under high temperatures was studied through numerical simulations of steady-state experiments. At 400 °C, the pretension of the bolt was only 67.3% of that at 20 °C. On this basis, a refined calculation formula for the high-temperature bolt pretension loss was proposed on the basis of the numerical results. The findings of this research can further improve the fire resistance design of prestressed steel structures.

Ultimate Resistance of Stiffened Curved Plates with Trapezoidal Stiffeners under Uniaxial Compression

Ultimate Resistance of Stiffened Curved Plates with Trapezoidal Stiffeners under Uniaxial Compression

Assessment of Strength and Deformation Characteristics of High-Strength Concrete in Structures and the Dynamics of Their Changes over Time

Based on the data from numerous production and laboratory tests, an analysis of the actual values of the main standardized strength and deformation characteristics of high-strength concrete of classes B60-B100 was carried out: ultimate resistance to axial compression, initial modulus of elasticity and Poisson’s ratio. It has been established that the values of prismatic strength (Rb) are close to cubic (R), and the ratio between them (prismatic strength coefficient) is not lower than 0.85. A comparison of Rb values with those calculated for limit states of the 1st group according to SP 63.13330.2018 shows that for concrete classes above B70 in the regulatory document they are unreasonably underestimated. The value of the coefficient of variation of high-strength concretes does not exceed 6.5%, which is predetermined by the features of their compositions, which ensure stability of consistency, segregation stability and technological reliability of concrete mixtures. The values of the initial elastic modulus (Eb) exceed the normative ones provided for by SP 63.13330.2018.The dependence of the values of the initial modulus of elasticity of concrete of the same class on the nature of the coarse aggregate has been established. According to experimental data, the elastic modulus can vary in the range of up to 19% depending on the characteristics of the coarse aggregate used. This variability of Eb is consistent with the recommendations of EN 1992-1-1:2004 Eurocode 2, but is not taken into account in SP 63.13330.2018. The time factor affects the change in the values of strength (R and Rb) and elastic modulus (Eb). According to the data obtained, in the period from 28 days to 1.5 years the increase in strength was 15–17%, elastic modulus – 8.8–9.8%. It has been established that changes in these characteristics over time are described by mathematical models and, accordingly, can be predicted depending on the age of concrete. The results obtained indicate that the standardized parameters of SP 63.13330.2018 do not fully take into account the service life of modern high-strength concrete, which makes it necessary to make changes to the specified document.

Study on thermo-mechanical properties of energy piles based on the improved exponential model

To further investigate the effects of temperature on the bearing capacity of the energy pile, the influence of soil temperature was considered and the pile top displacement corresponding to the ultimate side friction resistance of the energy pile was obtained. An improved exponential model that accounts for the influence of pile-soil temperature was developed. The feasibility of the model was verified through an indoor model test and numerical simulation. The results indicate that the error between the improved exponential model and the indoor model test was smaller compared with the numerical simulation. The maximum side friction error between the improved exponential model and the model test reached 0.8 % and 4.6 % at the end of the heating and cooling stages, respectively. The maximum additional thermal stress error between the improved model and the model test was 1.3% and 3.9% at the end of the heating and cooling stages, respectively. The error of the traditional and improved exponential model of additional thermal stress was 16 %. It is established that the improved exponential model was proved suitable for thermo-mechanical coupling analysis of energy piles. The temperature effect of the soil should be considered in the investigation of the energy pile.

Stochastic nonlinear inelastic analysis for steel frame structure using Monte Carlo sampling

This work comprehensively investigates the realistic ultimate resistance of steel frame structures based on the probability study model of input random variables due to uncertainty of material properties and geometric parameters. Four independent parameters and thirteen of their dependent components vary randomly in a variational range and seven scenarios of random combination are investigated by the probabilistic modeling, which incorporates the advanced inelastic analysis with direct Monte Carlo simulation. The analysis results for a typical example shows that the stochastic analysis result of steel frame's realistic ultimate resistance is lower than its deterministic analysis result, indicating that a stochastic analysis is needed to comprehensively qualify the safety of the structure. Moreover, a spectrum response, which is produced based on stochastic analysis, provides a better scientific solution.

Cross-sectional behaviour of QN1803 high-strength stainless steel I-section stub columns in fire

QN1803 is a novel high-strength stainless steel with low nickel. Compared to traditional stainless steel, QN1803 high-strength stainless steel has higher yield strength and lower cost without compromising anti-corrosion properties, thus leading to a wide application prospect. This paper focuses on the cross-sectional behaviour of QN1803 high-strength stainless steel I-section stub columns in fire. A total of eight stub column tests were finished, of which six were elevated temperature tests and two were room temperature control tests. Room temperature and elevated temperature tensile coupon tests were conducted to obtain the material properties of the QN1803 high-strength stainless steel. The design methods of European fire design standard EN 1993-1-2 and the latest fire design methods proposed by Xing et al., which will be incorporated into the upcoming version of EN 1993-1-2, were evaluated in terms of accuracy and safety for the fire design of QN1803 high-strength stainless steel I-section stub columns. It was found that most ultimate cross-sectional resistances of QN1803 high-strength stainless steel I-section stub columns predicted by the design rules of European fire design standard EN 1993-1-2 were unsafe, while the ultimate cross-sectional resistances predicted by the design methods of Xing et al. were safe and accurate for the tested QN1803 high-strength stainless steel I-section stub columns.

Numerical analysis of curved steel plate girders subjected to patch loading

Curved steel plate girders are often utilized in bridges built in congested urban areas, where intricate plan alignments are required. Their performance and design is, however, more complex than that of equivalent straight girders, especially regarding concentrated forces: while AASHTO adopts a simplified and empirical approach for the design of curved steel girders, the Eurocode for plated structures EN 1993-1-5 does not address the patch loading design of steel plate girders curved in plan, being only applicable to straight girders. Therefore, it is necessary to carry out further research in order to achieve a better understanding of the behavior of curved steel plate girders so that suitable design approaches accounting for the specific response of these structures can be developed. This paper presents a comprehensive numerical study on curved steel plate I-girders subjected to patch loading, considering material and geometric nonlinearities as well as initial imperfections. The numerical models are developed by means of the advanced finite element software ABAQUS and validated against experimental tests available in the literature. The numerical results demonstrate that the elastic critical buckling loads increase with increasing span-to-plan radii, which can be conservatively estimated using the EN 1993-1-5 provisions for straight steel girders, and that the ultimate patch loading resistance decreases with the radius of curvature. Based on this, practical recommendations are proposed to extend the applicability of the design provisions prescribed in the next version of EN 1993-1-5 for straight steel I-girders to the case of curved steel I-girders.

Experimental investigation on stiffened plates with non-continuous longitudinal stiffeners ending within the panel

The present contribution investigates a construction method predominately applied in crane manufacturing known as non-continuous longitudinal stiffening. In this approach, the longitudinal stiffeners end within the panel, leaving a gap before reaching the transverse stiffener or the end of the girder. Current standardization is limited to conventional continuous stiffening. Therefore, the present study conducts an experimental test series of 50 close-to-reality scaled, non-continuously longitudinally stiffened plates subjected to uniform compression to characterize their structural behavior. The results are compared regarding different geometry parameters. One main conclusion is that the gap drastically governs the ultimate resistance, usually leading to a triangular-shaped buckling mode.

Analytical and numerical studies on flexural resistance of fold-fastened multi-cellular steel panels

Fold-fastened multi-cellular steel panel (FMSP) is a novel type of cold-formed steel (CFS) built-up member, which is manufactured by connecting multiple FMSP cells. When connecting these cells, folded regions can be formed by lapping the FMSPs cells end to end, and indentations are used as fasteners during the manufacturing process. In this study, the flexural resistance of FMSPs was numerically and analytically investigated. Firstly, the refined finite element (FE) models were developed to simulate the flexural behavior of FMSPs. The accuracy of FE modeling method was validated by comparing the numerical results with experimental results obtained from the published literature about these investigations for CFS built-up members in terms of their moment capacities, moment-deflection curves and failure modes. Then, substantial parametric analyses involving a total of 105 different FE models of FMSPs were carried out to study the effects of steel thickness and strength, cellular dimension, width of fold-fastened regions and indented spacing on the flexural behavior of FMSPs. Finally, a sectional analysis based on the effective width method (EWM) was adopted to predict the ultimate flexural resistance of FMSPs. The results revealed that steel thickness and web plate depth have a great effect on the flexural behavior of FMSPs, while there was little influence on the ultimate load in other parameters. Moreover, the decrease in both width-to-thickness ratio and aspect ratio will lead to better ductile behavior for FMSPs. In addition, the EWM adopted in this study can agree well with the FE results, achieving better predicting results compared with other methods; therefore, this method is valid and well fits the practical needs.

Numerical and analytical investigations on punching shear performance of UHTCC-enhanced RC slab-column joints

The excellent tensile strain-hardening behavior of ultra-high toughness cementitious composite (UHTCC) makes it applicable for enhancing the punching shear performance of reinforced concrete (RC) slab-column joints. However, construction of an entire slab-column structure employing UHTCC would inevitably lead to uneconomical designs. To balance the economic benefits with the punching performance, utilizing UHTCC in the core region of a slab-column joint is a promising approach. In this study, the impact of UHTCC application range (UAR) on the punching shear performance of UHTCC-enhanced RC slab-column joints (USCJs) was investigated, and an approach for determining the optimal UAR was also presented. Two USCJ specimens with different UAR were tested, and experimental results were compared with the counterpart numerical results to validate the finite element (FE) models. Twenty FE USCJ models with different UAR were established. Then the impact of UAR on development of critical cracks, ultimate resistance, and ductile behavior was examined. Analytical approaches based on the critical shear crack theory as well as on the combination of critical shear crack theory and yield line theory were adopted to predict the ultimate and flexural resistances, respectively. The failure mode was determined by comparing these two resistances and considering the ductile coefficient, based on which the effect of UAR on the failure mode was determined. The results show that the location of critical shear cracks and the appearance of flexural cracks vary with UAR. By increasing UAR, the ultimate resistance increases, but the ductile coefficient first increases and then slightly decreases. Provided that the UAR is increased to some extent, the growth rate of the ultimate resistance evidently slows down and the ductile coefficient peaks, indicating the optimal UAR considering both the economic efficiency and the punching performance. The presented approach shows promise for determining the optimal UAR in practical engineering designs.

Design-truck ultimate limit states of buried modular polymer stormwater collection structures

Modular polymer stormwater structures are a relatively new class of buried structure with two horizontal platens supported by vertical columns. While structural demand at design truck loads has been quantified, the ultimate limit state to design truck loading is unknown. Full-scale physical experiments were conducted to quantify the applied load and identify the mode(s) of failure at the ultimate limit state of three types of modular structures when buried (with 0.6 m soil cover) and subject to static design truck loading. All three module types tested reached an ultimate limit state at applied loads around three times the nominal design load but had different modes of failure. The ultimate resistance for the module with columns having the lowest moment of inertia relative to length squared was caused by column buckling and top platen rupture, while the two modules with nearly twice the moment of inertia relative to length squared failed by top platen rupture and their column forces at most were 70%–75% of their short-term single column buckling resistance. The results provide new data to allow independent load rating of the buried structure, support continued assessment of column buckling, and identify the need to limit platen bending deflections.

P-y Curve for Estimation Lateral Bearing Capacity of Single Bored Pile in Overconsolidated Soils Using The Three-Dimensional Finite Element Method.

The p-y curve method is widely used to predict piles’ lateral bearing capacity. It assumes independent springs with a non-linear modulus of subgrade reaction for analyzing soil resistance (p) and deflection (y). This study determined the lateral bearing capacity using the three-dimensional finite element method (FEM-3D) and finite difference method (FDM), which was later compared with the loading test results. Therefore, the pile head condition is assumed to be the free-head. To determine the lateral bearing capacity, input the lateral deflection at the pile head. In FEM-3D, the pile and lateral deflection in the pile head is modeled using cluster elements and surface-prescribed horizontal displacements, respectively. On the other hand, in FDM, pile heads and boundary conditions are modeled using displacement and moment. The results of the lateral bearing capacity using FEM-3D provide predictions that are close to the loading test, with a difference of about 4.2%. In contrast, the FDM method produced conservative results due to its reliance on semi-empirical formulas. The ultimate soil resistance (Pult) formula in FDM is more suitable for rigid-pile behavior. The prediction of lateral bearing capacity using FEM-3D provides more accurate results due to its ability to model complex soil-pile interaction. The stress history, soil-pile interaction, and more reliable constitutive models can be modeled in FEM-3D.

Ultimate tensile resistance of steel angle members connected by one leg with bolts

Ultimate tensile resistance of steel angle members connected by one leg with bolts

Axial compressive performance and design of multi-celled corrugated-plate CFST walls

The corrugated steel plate has been widely used in steel and composite structures due to its large out-of-plane flexural stiffness. An innovative type of steel–concrete composite wall using corrugated steel plates called multi-celled corrugated-plate concrete-filled steel tubular (MC-CFST) wall has been proposed recently. In order to study its performance under axial compression, numerical analysis was conducted in this paper. A refined finite element (FE) model was established and validated by previous test results. The vertical and out-of-plane normal stresses of concrete and strains of corrugated steel plates were analyzed, indicating that the corrugated steel plates had a good confinement effect on the infilled concrete. Then, a parametric analysis was conducted to investigate the effect of various parameters on the axial compressive performance of MC-CFST walls. The main parameters included corrugated cell width, wall depth, thicknesses of corrugated steel plates and steel tubes, concrete and steel strengths and corrugation amplitude. Finally, the equivalent confinement factor ξw was defined to evaluate the confinement effect of corrugated steel plates on the infilled concrete. On this basis, a design formula for calculating the ultimate resistance of the MC-CFST wall was proposed. The proposed formula exhibited good agreement with experimental and numerical results, and it could provide valuable references for the design of MC-CFST walls in practice.

Study on p-y curve of large diameter pile under long-term cyclic loading

The pile foundation used in offshore wind turbine system is located in a complex marine environment and is subjected to various long-term cyclic loads such as wind, wave and current. However, the attenuation effect of long-term cyclic load on seabed soil has not been considered by most of the existing p-y curve calculation models. In order to solve this problem, the finite element numerical model of pile-soil interaction of large diameter single pile foundation of offshore wind turbine is established in this paper. Based on the Stokes second-order wave theory, the time history curve of wave and current loads on piles with different diameters are derived and calculated by programming. Then the soil stiffness attenuati on model subjected to marine cyclic loading is embedded into the finite element model by subroutine. Considering the influence of the number of ocean load cycles on the ultimate soil resistance of the soil around the pile and the initial foundation reaction modulus, the calculation results of different pile diameters and soil depths are analyzed and regressed. Finally, the p-y curve calculation model of large diameter single pile foundation of offshore wind turbine under long-term ocean cyclic load is obtained.

Behavior of novel steel-concrete-steel sandwich walls under low-velocity impact loading

This paper reported experimental and analytical studies on impact behaviors of steel-concrete-steel sandwich composite (SCSSC) walls using enhanced C-channels (ECs). Six SCSSC walls, designed with variations in impact energy levels and boundary columns, were tested by drop hammer and simulated by LS-DYNA. The main failure modes of the specimens after impact loading were global flexure and flexure-shear mode. As direct-link connections, the ECs provided strong interfacial shear and tensile resistances, which prevented local failure of SCSSC walls. Under three impact energy levels, boundary CSFT columns increased the ultimate impact resistance of SCSSC walls, and effectively reduces their peak displacements. Refined finite element (FE) models considering the effect of strain rate were established, and verified by reported impact test results. In addition, this study adopted modified two-degree-of-freedom (TDOF) model to estimate the impact force and displacement responses of this type of SCSSC walls. Validations against reported test results confirmed that the TDOF model provided reasonable predictions.