Existing Design Codes Research Articles

Predicting load capacity of shear walls using SVR–RSM model

Accurate prediction of the shear capacity of reinforced concrete shear walls (RCSW) is essential for the wind and seismic design of buildings. However, due to the diverse structural configurations, multitude of load scenarios, and highly nonlinear relations between the design parameters and the shear load capacity, this prediction is very complex. Existing pertinent design code provisions such as the American Concrete Institute ACI-318 and the Eurocode rely on empirical expressions that have various limitations and attain low predictive accuracy. Hence, in this paper, we pioneer a novel hybrid intelligent model to predict the ultimate shear capacity of RCSW. The support vector regression (SVR) and response surface model (RSM) were coupled based on two calibrating strategies in a novel hybrid modeling approach called RSM–SVR. The accuracy, tendency and uncertainty of the proposed SVR–RSM model along with that of three existing empirical relations and two design code provisions were assessed using various statistical metrics based on a comprehensive experimental database retrieved from the open literature. The existing design codes and empirical models were found to be inflicted with high variability and did not capture the influence of the key design parameters on the shear capacity in a robust and rational manner. Conversely, it is shown that the proposed RSM–SVR modeling approach achieved superior accurate predictions for the shear strength of RCSW. The proposed RSM–SVRmodel enhanced RMSE for the training (testing) dataset by 510% (150%) compared to the Baghi et al. model, 550% (190%) compared to the ACI 318-14 design code, 530% (155%) compared to the Chandra et al. model, 320% (145%) compared to the RSM model, and 450% (90%) compared to the SVR model. The novel approach also better captured the influence of the key design parameters, demonstrating robust tendency and much lower uncertainty. Thus, the proposed novel model could be harvested in intelligent generative design and for the enhancement of pertinent provisions in design codes. The proposed method achieves outstanding performance, while maintaining superior computational efficiency and low run time.

Compressive and thermal properties of foamed concrete at high temperature

Foamed concrete is an attractive material for structural use and insulation of buildings, which can replace flammable organic insulating materials on the market. This study investigated the compressive and thermal properties of the plain, fly ash and expanded polystyrene (EPS) foamed concrete ranging widely in density from 180 to 1800 kg/m3. Furthermore, the compressive strength of the plain foamed concrete was analyzed at four density levels of 180, 325, 450, and 595 kg/m3 and at four temperatures of room temperature, 300, 600, and 900 °C to quantify its fire resistance. The compressive strength of the foamed concrete dramatically declined, and it suffered severe damage when the temperature was higher than 300 °C. A constitutive stress–strain model incorporating the compressive strength–density relationship and the temperature effects was also proposed for the plain foamed concrete. The findings may provide new perspectives on the existing design codes for energy efficiency and fire protection.

Column base connections under compression and biaxial moments: Experimental and numerical investigations

Very little guidance exists on the design of steel column base connections subjected to axial compression and biaxial bending moment. In order to develop a design method, an experimental program of 32 tests to failure was carried out to determine the effects of various factors that affect the failure modes, strength and behaviour of unstiffened column base connections under biaxial bending moment. Plate thickness, bolt diameter and axial compression force were set to low and high values in a full factorial experimental design chosen to bring about different failure modes. The program was completed with detailed finite element analyses calibrated with the experimental results. The investigations provide a clearer understanding of the failure modes, strength and behaviour of baseplates under biaxial bending moment. Increases in plate thickness, holding-down bolt diameter and axial force were found to increase the connection strength. The welds at the flange tips of corner bolted base connections under biaxial bending were shown to be vulnerable to premature failure, and the work showed that existing design codes are conservative for the uniaxial bending case.

Effects of steel fibers on failure mechanism of S-UHPC composite beams applied in the Arctic offshore structure

A novel steel–concrete–steel composite structure constructed using ultra high-performance concrete (forming an S-UHPC composite structure) was applied in Arctic offshore structures. This type of structure can withstand ice pressure derived from impinging sheet ice in the Arctic region. In this study, the failure mechanism of S-UHPC composite beams was explored experimentally and analytically, considering the effects of steel fibers in UHPC. Five groups of push-out tests were conducted to reveal the interfacial performance between steel plates and UHPC. Static tests on S-UHPC composite beams were performed to study their structural behaviors. The results indicate that steel fibers have a significant effect on the failure modes, slippage behavior, and mechanical behavior of the S-UHPC composite beams. Furthermore, on the basis of test results, finite element (FE) models of the push-out tests and static tests of the S-UHPC composite beams were developed and validated. Further, a parametric study was carried out to summarize the failure modes of the push-out tests and to explore the influence mechanism of steel fibers on the structural behavior of the S-UHPC composite beams. Finally, an analytical model for predicting the ultimate strength of S-UHPC composite beams was proposed and compared with existing design codes.

A comparative study and a simplified formula for punching shear design of concrete slabs with or without membrane tensile forces

Punching shear failure of concrete slabs is brittle with very little warning, whether with or without membrane tensile forces. Tensile forces decrease the punching shear strength, which if not accounted for properly causes a premature failure. In addition, there is a lack of agreement between various design codes for the case of punching shear, whether with or without membrane tensile forces. The study aims to examine and refine the punching shear design of concrete slabs with or without membrane tensile forces. A state-of-the-art review of six decades of experimental testing of and models for RC elements subjected to punching shear with or without membrane tensile forces was conducted. In addition, the accuracy, consistency, and safety of the design provisions are assessed. Moreover, concluding remarks were outlined, which could be helpful in further development of existing design codes. Last but not least, an existing simplified punching shear strength formula for lightweight concrete slabs was adapted, further modified, proposed, and validated for normal-weight RC slabs with or without membrane tensile forces. The proposed formula is simple, yet accurate and makes physical sense as well as being compatible with the Critical Crack Theory.

Wind induced response of corner modified 'U' plan shaped tall building

In the present study, the well-adopted practice of minor aerodynamic modifications (chamfered corner and rounded corner) has been introduced on widely used irregular U plan shaped tall building to minimize the wind induced responses and also to give a good aesthetics. The necessary design inputs for a wind resistance design such as force coefficient and pressure coefficients have been well explored and illustrated graphically to provide a complete guideline to the designer. The randomness of wind directionality has a significant impact on tall structures, which is generally not detailed in existing design codes, is incorporated by considering wind directions ranging from 0° to 180° at an interval of 15°. Computational fluid dynamics (CFD) has been utilized to simulate wind flow using two turbulence models, i.e., k-epsilon and Shear Stress Transport. The model has been validated by comparing the results of a published research article on a U-shaped building without corner modification. The grid independence study has been done to check the reliability and accuracy of the analysis results. Since such study of wind directionality on corner modified U-shaped building is not observed in the existing literature, it constitutes the uniqueness of the present study. A significant reduction in force coefficient has been achieved by implementing modification, but the faces of those updated corners mostly been attracted by excessive pressure. This indicates the necessity of proper cladding configurations. The rounded corner buildings are turning out to be more effective when compared to the chamfered corner for reducing wind load.

Flexural Strength Evaluation of Multi-Cell Composite T-Shaped Concrete-Filled Steel Tubular Beams.

The multi-cell composite T-shaped concrete-filled steel tubular (MT-CFST) element is an innovative structural form. It has great potential for construction applications because of favorable advantages over traditional composite elements. The flexural strength of MT-CFST beams was investigated in this study to provide recommendations in line with existing design codes. First, formulations to evaluate the flexural strength of MT-CFST beams were derived based on the Unified Theory and plastic stress distribution method (PSDM). For the Unified Theory-based formula, a modified confinement effect factor that considers the shape of a cross-section was proposed. An experimental study on the flexural behavior of six MT-CFST beams as well as two hollow section counterparts was conducted. The influence of bending moment direction, concrete infill, wall thickness, and cross-section sizes were investigated. The accuracy of the proposed formulations was verified against the test results and numerical results from finite element modeling. The comparisons showed that the formula in line with the Unified Theory provided more accurate predictions with reasonable conservatism for the studied MT-CFST beams.

Compressive behaviour of circular CFDST short columns with high- and ultrahigh-strength concrete

Concrete-filled double-skin steel tubular (CFDST) columns possess lower self-weight, higher ductility and energy absorption than conventional concrete-filled steel tubular (CFST) ones. The use of high-strength concrete (HSC) can further enhance their advantages, such as greater mechanical and economical benefits. However, there is little information on the structural performance of CFDST columns with HSC, especially ones with ultrahigh-strength concrete (UHSC). In this paper, a comprehensive experimental program consisted of 24 specimens was carried out to investigate the compressive behaviour of circular CFDST short columns with HSC and UHSC. The test results show that CFDST columns with higher strength concrete generally achieve higher initial stiffness and axial strengths but lower ductility. Additionally, the axial strengths of CFDST columns are improved as the yield stress and wall thickness of the outer steel tubes increase and as the hollow ratio decreases. A finite element (FE) model was established and verified against the present test results, based on which the interaction of the steel tubes and concrete and the load distribution on components were analysed. A parametric study using the verified FE model was conducted to further ascertain the influences of column variables on the compressive behaviour of the studied CFDST columns. Finally, the applicability of the existing design codes and empirical models to design the CFDST columns was evaluated based on the test results in the present and previous studies. It is shown that European code EN 1994−1−1 (EC4) achieves better strength predictions than other design models.

Analytical Modelling of LACFCST Stub Columns Subjected to Axial Compression

This paper presents a numerical investigation of lightweight aggregate concrete-filled circular steel tubular (LACFCST) stub columns under axial compression. A finite 3D solid element model of the LACFCST stub column was established by adopting a plastic-damage constitutive model of lightweight aggregate concrete (LAC). The finite element model (FEM) analysis results revealed that the confinement effect of the steel tube on the infilled LAC was weaker than that on the infilled conventional concrete. A parametric study making use of 95 full-scale FEMs was conducted to investigate the influences of various design parameters of LACFCST stub columns on their ultimate axial bearing capacity and the composite actions. Moreover, a numerical model of the axial and transverse stress of steel tubes at the ultimate state of LACFCST columns was proposed using the regression method. Based on the equilibrium conditions and the proposed model, a practical design formula making use of an enhancement factor was derived to estimate the ultimate bearing capacity of LACFCST stub columns by using the superposition method. The validity of the proposed formula was verified against the experimental data of 49 LACFCST stub column specimens under the axial loading available in the literature. Meanwhile, the accuracy and conciseness of the proposed formula were evaluated by comparison with the formulas suggested by the existing design codes.

New analytical method for computing moment redistribution in RC beams under concentrated load

ABSTRACT Computing the moments in RC structures after the yield by linear elastic analysis can lead to an inaccurate assessment of the behaviour due to the nonlinear behaviour. Therefore, it can become necessary to use more advanced methodologies to achieve a higher degree of performance optimisation of structures than those resulting from the simplified approaches adopted by existing design codes based on linear elastic analysis with redistribution of internal forces. The moment redistribution is supposed to start after occurring the cracks of concrete, but with small ratio. In this study, the moment redistribution before the yielding will be neglected, and the redistribution is focused after the yield. This paper suggests a mathematical model to investigate the moment redistribution in RC beams after yielding analytically. In the suggested mathematical model, the beam after forming the plastic hinges is converted into a virtual beam that can be analysed by structural linear analysis. The plastic hinges in the virtual beam will be represented as rotational springs having a linear rotational stiffness against the induced moment. The actual moments can be found through derived relationships in the mathematical model between it and the virtual moment. The mathematical model was verified and it gave values of moment matching experimental results. Also, a comparison for degree of moment redistribution among the suggested mathematical model and several design codes was performed. The analytical results indicate that the proposed mathematical model can be used for analysis of moment redistribution of RC beams.

On-Site Experimental and Numerical Investigations of Latticed Girder Composite Slabs

In this study, on-site bending experiments which represented realistic and pragmatic engineering applications were performed to investigate the resistance, deflection, and cracking process of latticed girder composite slabs. Then, utilizing ABAQUS software, nonlinear finite element (FE) models were established to investigate the behavior of the slabs. The modeling took into account the contact between the precast and cast-in-place concrete interfaces. Additionally, a damage-cracking methodology was introduced to evaluate the crack opening width of the slab. The results demonstrated that the proposed numerical model was capable of reproducing the typical behavior of the composite slabs’ performance analysis. The experimental and numerical results demonstrate that the lattice girder composite slabs conformed to the requirement of existing design codes.

Seismic Performance of A Bolt-assembled Precast Panel Building with DfD: A Quasi-static Test and Discussion on Existing Design Codes

ABSTRACT The seismic performance of a two-story building was investigated through a small-scaled quasi-static test. The test results show that the bolt-assembled PC panel building system can present reliable structural integrity, including transferring shear action and performing deformation ability. Based on the results, the failure mode and force-transfer mechanisms of the system were discussed and a modified design model was proposed to calculate the resistant capacity of bolt joints based on the current design code. The paper pointed out that the drift limits suggested in the current code may not suitable for evaluating the damage state of the system.

Experimental and Numerical Study of Lattice Girder Composite Slabs with Monolithic Joint

This paper studies the behavior of lattice girder composite slabs with monolithic joint under bending. A full-scale experiment is performed to investigate the overall bending resistance, deflection and the final crack distribution of latticed girder composite slab under uniformly distributed load. A finite element model is given for the analysis of the latticed girder composite slabs. The effectiveness and correctness of the numerical simulations are verified against experimental results. The experimental and numerical studies conclude that the lattice girder composite slabs conform to the requirement of existing design codes. A parametric study is provided to investigate the effects of lattice girder with following conclusions: (a) the lattice girder significantly increases the stiffness of the slab when comparing with the precast slab without reinforcement crossing the interface; (b) the additional reinforcement near the joint slightly increases the stiffness and resistance, while it prevents damage near the joint.

Experimental and numerical investigations of circular recycled aggregate concrete-filled stainless steel tube columns

This paper reports a comprehensive experimental and numerical study of the flexural buckling behaviour and resistances of circular recycled aggregate concrete-filled stainless steel tube columns. The experimental programme, adopting four series of column specimens designed with various stainless steel tube sizes, recycled coarse aggregate replacement ratios and member lengths, included material tests on both recycled aggregate concretes and stainless steel tubes, initial global geometric imperfection measurements and pin-ended column tests. The obtained experimental results, including the failure loads, load–mid-height lateral deflection curves and flexural buckling failure modes, were reported in detail. The effects of the stainless steel tube size, recycled coarse aggregate replacement ratio and member length on the flexural buckling resistances of the column specimens were examined. The lateral deflection distributions along the column specimen lengths and the development of the longitudinal strains of the outer stainless steel tubes were discussed. The experimental programme was supplemented by a numerical modelling programme, in which finite element models were developed and validated against the test results and then used for conducting parametric studies to generate further numerical data over a wide range of cross-section dimensions and member lengths. Given that there have been no existing design codes for recycled aggregate concrete–stainless steel composite structures, the relevant codified design rules for circular natural aggregate concrete-filled carbon steel tube columns failing by flexural buckling, as used in Europe, Australia/New Zealand and America, were assessed for their applicability to circular recycled aggregate concrete-filled stainless steel tube columns, based on the test and numerical data. The assessment results revealed that the design rules, as given in the Australian/New Zealand standard and American specification, result in unsafe flexural buckling resistance predictions when used for circular recycled aggregate concrete-filled stainless steel tube columns, while the Eurocode design rules lead to more safe and accurate flexural buckling resistance predictions.

A machine learning-based formulation for predicting shear capacity of squat flanged RC walls

The squat flanged reinforced concrete (RC) walls have been widely utilized in nuclear power plant and building structures. Nevertheless, the empirical equations in current design codes and published studies show a significant discrepancy in calculating the shear strength of the walls. The purpose of this study is to develop an effective machine learning model, namely artificial neural network (ANN), for predicting the shear strength of squat flanged RC walls. A total of 369 test results of squat flanged RC walls were collected from the literature and used to develop the ANN model. The results of the proposed model were compared with those of existing design codes and published studies. The comparisons emphasized that the developed ANN model in this paper can predict the shear capacity of squat flanged RC walls more accurately than the existing equations. Moreover, the effect of input parameters on the predicted shear capacity of the walls was sufficiently investigated. A predictive formula based on the ANN model, which can cover thirteen input parameters, was then proposed to compute the shear strength of the squat flanged walls. Additionally, an efficient graphical user interface (GUI) platform has been established for facilitating the practical design process of the squat flanged RC walls.

Effect of concrete unit weight on the mechanical properties of bottom ash aggregate concrete

The depletion of natural aggregates has already progressed significantly in some regions and countries, including South Korea, and it is critical to identify replacement materials to address this problem. In recent decades, researchers have focused on low-cost industrial residues or solid waste as potential solutions, and this study involves application of bottom ash (BA), a byproduct of coal-fired electrical power plants, as fine and coarse aggregates. The application of BA to the manufacture of concrete is noteworthy in terms of economic as well as ecological aspects for preserving natural resources. In the experiment, a total of 20 concrete containing bottom ash (CCBA) mixtures classified according to W/C and the bottom ash aggregate (BAA) mixing ratios were evaluated for their workability and various mechanical properties. The results of the experiment showed that the factor having the greatest effects on the mechanical properties of concrete was the usage of coarse BAA or lack thereof, and that the rates of decline in mechanical properties due to the replacement of fine BAA were within levels that could be controlled by other design factors, such as W/C. This study provides a comparison between the experimental results and the prediction results of several existing design codes, which will serve as basic data for proposing a reliable, predictive CCBA structural design model.

Essential state-of-stress features of HBBC connections revealed by modeling simulative strain energy

This study reveals the essential working features of H-beam-to-box-column (HBBC) steel connections applying structural state-of-stress theory. Firstly, a finite element convergence criterion is proposed to judge the simulative ultimate loads of the HBBC connections. Then, the state-of-stress mode and the parameter characterizing the mode are built using the simulative strain energy data. As a result, the Mann-Kendall (M-K) criterion detects the essential and inevitable working behavior feature complying with the natural law from quantitative change to qualitative change of a system, which reveals the starting point in the failure process of the HBBC connection. The failure starting point redefines the HBBC connection’s failure load and its calculating formula is fitted considering three configurational parameters of angle. Referring to the failure load, the M-K criterion identifies the elastic–plastic branch (EPB) point of the HBBC connection from its state-of-stress evolution. Both failure load and EPB load provide the significant reference to the improvement on the existing design codes of connections with the rational safety margin and without the over conservation of the traditional stress capacity design load.

Calculation of displacements and internal forces of anchored retaining piles.

Pile-anchor retaining structures are widely used in excavation engineering. The evaluation of lateral displacements, the internal forces of piles are extremely important for the performance of the structure. Most of the existing methods are empirical, semiempirical or FEM methods, while analytic calculation methods for this evaluation are rare. This paper presents an analytic method to calculate the displacements and internal forces of anchored retaining piles based on the existing design code. In the calculation method, the singular function is applied to evaluate the effect of segmented loading on the deflection of a beam with a nonuniform cross section. The load concentration function, expressed by the singular function, can describe the segmented load and be integrated without a complicated procedure for determining the integral constants. The method is applied to a structure in Wenzhou, China, and the calculation results are compared to the field measurement results. This method is only valid for pre-failure predictions.

Behavior of three-chord concrete-filled steel tube built-up columns subjected to eccentric compression

An experimental investigation of a series of three-chord concrete-filled steel tube (CFST) built-up columns was conducted under eccentric compression. The influences of slenderness ratio, eccentricity ratio, eccentricity direction, and brace pattern (battened or laced) on the load bearing process, failure modes, and ultimate load-carrying capacities of the specimens were analyzed. The test results indicate that a CFST built-up column exhibits better performance than a corresponding plain steel built-up column. The ultimate strengths and stiffnesses of the three-chord CFST built-up specimens decreased with increasing slenderness ratio or eccentricity ratio. Battened specimens exhibited lower load-carrying capacities than laced specimens, and different load-bearing capacities were obtained for specimens under different directions of compression eccentricity. Using the proposed equivalent slenderness ratio, three existing design codes were evaluated to predict the stability coefficient, and a new correlation equation considering two failure modes is suggested for calculating the ultimate strength of three-chord CFST built-up columns subject to combined compression and flexure.

Behavior of FRP wrapped concrete filled steel tubular columns

ABSTRACT During earthquake loading, concrete filled steel tubular (CFT) columns subjected to buckling at plastic regions. To control these type of buckling, a new technique is imposed in this research work. Therefore, an additional transverse confinement using carbon fiber reinforcement polymer (CFRP) laminates are wrapped around the CFT columns. An experimental study was conducted on FRP wrapped concrete filled CFT (CCFT) columns. The test variables are thickness of steel tube, different grades of concrete, and number of layers of FRP laminates. Experimental results of CFT columns were compared with computed load carrying capacity of the existing design codes. Of all the codes compared, DL/T 1999 showed the least variations and is found to be more viable to predict ultimate load carrying capacity of CFT columns. Load strain plots obtained from experimental study reiterate the fact that CCFT columns wrapped with two layers of CFRP showed enhanced strength and ductility compared to other CCFT columns. The failure modes of CCFT columns were observed during experimental study.