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Axial load and biaxial bending strongly influence the deformation capacity of column cross-sections, in most cases causing a non-negligible loss of curvature and ductility with respect to the case of pure bending along principal axes, commonly assumed as the basic condition to assess the inelastic capacity. In consideration of this the paper investigates the biaxial deformation performance of RC rectangular cross-sections belonging to one-dimensional elements, focusing on the influence of some parameters as the cross-section aspect ratio and the distribution of the rebars, as well as the mechanical characteristics of concrete and steel and the impact of biaxial/axial stresses. In the paper ultimate curvature domains, yielding curvature domains and ductility domains as novel assessment tools are provided. The deformation performance of the cross-sections, represented by the above domains, is discussed through a parametric study on the sensitivity of the domain shape to the major governing geometrical and mechanical factors. Further the role of axial load in terms of capability to level out the deformation capacity associated to different planes of bending is highlighted. Finally, a definition of specific biaxial ductility indicators is provided. The latter are proposed as measures to classify the biaxial deformation capacity associated with rectangular RC cross-sections for an engineered design. [ABSTRACT FROM AUTHOR]

This paper introduces an application (based on the algebraic methods) that can be used to evaluate the stress and strain time evolution of concrete compact cross-sections cast and/or prestressed in consecutive stages and exposed to long term loading. The overall cross-section may consist of a concrete, structural steel or fibre reinforced polymer component combined with the original concrete cross section at a distinct stage of the construction period or during the life of the structural element. Moreover, the cross-section can be prestressed both before and after gaining the final shape. Therefore, the application suggested in this manuscript applies to new structures cast in consecutive stages, and to specific problems involved with the rehabilitation or strengthening of concrete structures. The problem is solved by means of the force method and McHenry’s superposition principle. In a following paper, a series of examples will be utilised to verify the accuracy of the application presented in this document. The results obtained by the method described in this manuscript will be compared to a refined and complex general approach introduced in a previous paper. [ABSTRACT FROM AUTHOR]

In this paper attention is focused on the uprights, i.e. vertical elements of the skeleton frames of steel storage rack systems. Their response is quite difficult to predict because of the significant influence of the interaction between local, distortional and overall buckling phenomena, owing to the presence of open mono-symmetric thin-walled cold-formed cross-sections. As a consequence, very high engineering competences are necessarily required to guarantee relevant load carrying capacities with structural systems of extremely limited weight and of very modest costs. Design provisions admit few alternatives, leading to different sizes and weight of the racks and, as consequence, to different degrees of economic competitiveness on the market. In the framework of a more general research project on steel storage rack structures, three options of designing the uprights in Europe have been investigated in the present paper. Several cases from practice have been selected, which comprise of uprights differing for cross-section geometry, slenderness and load conditions. A suitable finite element program for academic use characterized by a refined beam formulation capable of capturing key features of uprights has been used to model the elastic buckling interaction between the axial load and the bending moment. Non-negligible differences have been detected for what concerns the admitted design approaches in terms of beam–column load carrying capacity; furthermore, the direct comparison of the research outcomes offers practical indications for an optimal use of the material in accordance with the required safety standards. [ABSTRACT FROM AUTHOR]

Abstract: Fire events in enclosures (such as tunnels) can have severe influence on the safety of support structures, characterized by severe fire loading as regards both the speed of temperature rise and maximum temperatures. This paper contains results of real-scale fire tests, comprising temperatures within the tested concrete cross-section, deformations and rotations at various locations as well as the extent of spalling. Monitoring of cracks during and after fire loading completes the experimentally-obtained data. Based on the collected data, validation of numerical tools for the assessment of the safety of underground support structures, as presented in Part II of this paper, becomes possible. [Copyright &y& Elsevier]

Highlights • Octagonal, circular and square tubular steel stub columns were tested under compression. • Finite element models were developed and verified by the test results. • Cross-section classification in design codes were assessed by the tests and FE results. • A new cross-section slenderness limit and an alternative design approach were proposed. Abstract This paper presents an experimental investigation on the compression behaviour of cold-formed octagonal, circular and square tubular steel stub columns. Three octagonal hollow steel tubes were examined under axial compression while three circular steel tubes and two square steel tubes were tested for comparison. Nine existing test data on octagonal hollow steel tubes were also collated for comparison. The hollow tubes were fabricated by welding two cold-formed half-section steel plates. To examine the material characteristics, flat, curved and corner coupons were extracted and tested. Residual stress distribution in longitudinal direction was also measured by sectioning method. Fifty longitudinal strips with a nominal width of 10 mm were machined by a wire cutting machine. The test results obtained from the tensile coupon tests and residual stress measurements were examined to evaluate the effect of the fabrication process on different cross-sectional shapes. The geometric imperfections of each specimen were carefully measured. Cross-sectional capacity, load-deformation relationships and failure modes of the stub columns were presented by the stub column tests. Finite element model was developed and validated against the experimental results. The experimental cross-sectional capacities were accurately predicted by the finite element models. The test data accompanied with the FE results were assessed with reference to current design provisions on cross-section classification and a suggested cross-section slenderness limit and an alternative design approach for octagonal cross-sections were proposed. [ABSTRACT FROM AUTHOR]

Highlights • Efficient static and dynamic analysis of jointed Euler-Bernoulli beams. • Step changes in material and cross-section. • Internal rotational, internal translational and external translational springs. • Free and forced vibration of jointed Euler-Bernoulli damped beam. • Closed-form expressions of the four integration constants. Abstract Many engineering systems can be modelled as an assembly of beams with different material properties and cross-sections jointed at their edges. This paper presents an approach to analyse jointed Euler-Bernoulli (EB) beams with step changes in material and cross-section under static and dynamic loads. The standard approaches to tackle this type of problem are not completely satisfactory in terms of: (i) computational efficiency in dealing with step changes in material and cross-section, when the continuity conditions must be enforced with auxiliary equations (classic approach) or when a denser mesh has to be used at the discontinuity interfaces (Finite Element Method); (ii) taking into account efficiently internal and external springs at the discontinuity interfaces; (iii) numerical errors in the evaluation of high-order modes for jointed beams. An approach is proposed to overcome these limitations. This approach tackles an assembly of n piecewise homogenous EB beams jointed at their edges using the generalised functions to obtain a single expression of the solution which depends on the 4 integration constants associated with the boundary conditions. Closed-form expressions of the 4 constants are provided. Further, in the presence of internal or external springs, additional constants representing the discontinuities have to be taken into account. The latter are computed by considering one additional condition for each discontinuity. The proposed approach is particularized for the static and dynamic analysis (modal analysis and forced vibration analysis). The feasibility of the proposed approach is shown with two numerical applications. [ABSTRACT FROM AUTHOR]

Abstract: For structural optimization problems, such as the weight minimization of steel framed structures, the sizing design variables are often defined as the cross-sectional areas of the members, which are to be chosen from commercially available tables such as those provided by the American Institute of Steel Construction. Alternatively, the cross-section dimensions, , , and (which may be discrete or continuous) can be defined independently for each profile. This paper discusses the structural optimization problem of framed structures involving sizing design variables where a special genetic algorithm encoding is proposed in order to establish a strategy to discover ideal member grouping of members. Advantages in fabrication, checking, assembling, and welding, which are usually not explicitly included in the cost function, are thus expected. The adaptive penalty method (APM) previously developed by the authors is applied to enforce all other mechanical constraints considered in the structural optimization problems discussed in this paper. [Copyright &y& Elsevier]

Highlights • Material properties of cold-formed steel semi-oval hollow sections were examined. • Cross-sectional behavior was studied through stub columns. • Experimental and numerical investigation of semi-oval hollow sections was conducted. • Continuous Strength Method was modified for semi-oval hollow section stub columns. Abstract This paper presents an investigation on the material properties, residual stress distributions and cross-sectional behavior of cold-formed steel semi-oval hollow sections. Four cross-section series were included in the test program. The test specimens were cold-formed from hot-extruded seamless steel circular sections. Tensile coupon tests were conducted on coupon specimens extracted from three critical locations, namely the flat, curved and corner portions, of each cross-section as well as half of the cross-section of a representative section. Membrane and bending residual stresses distributions on the representative section were measured in both longitudinal and transverse directions. In addition, initial geometric imperfections were measured for each cross-section series and stub column tests were conducted to determine the average stress–strain relationship over the complete cross-section in the cold-worked state and to examine the cross-sectional behavior of cold-formed steel semi-oval hollow sections. Furthermore, a finite element model was developed and validated against the test results. With the verified finite element model, an extensive parametric study over a wide range of cross-section geometries was performed. The load-carrying capacities of stub columns obtained from experimental and numerical investigation were compared with the design strengths predicted by the Direct Strength Method using the design equations originally developed for open sections and the Continuous Strength Method with the design curves originally developed for traditional tubular sections. The comparison results show that the existing design methods provide conservative design strength predictions. In this study, modification on the Continuous Strength Method is proposed, which is shown to improve the accuracy of the design strength predictions in a reliable manner. [ABSTRACT FROM AUTHOR]

This paper analyzes lateral-torsional buckling (LTB) of elastic beams with rectangular cross section having constant thickness, and depth symmetric with respect to the midpoint and tapered linearly in each half with smallest depth at the midpoint. This type of butterfly-shaped beam is used as a shear link in steel plates that serve as structural fuses to reduce the seismic response of buildings. LTB has been observed in previous quasi-static tests and found to be a critical limit state. The ends of the beam are prevented from twisting and can be assumed to be pinned with respect to bending in the weak direction. Numerical results are obtained for LTB of butterfly-shaped beams with the use of a shooting method assuming uniform torsion. Pure bending, reversed moments, and end moments with unequal magnitudes are investigated first. A compressive load is included next, and interaction curves for combinations of critical moment (squared) versus axial load are determined. Finally, the effect of in-plane shear deformation on LTB is examined. Plots showing the influence of various parameters are presented, along with some analytical approximations for the critical moment in terms of geometric and material quantities. [ABSTRACT FROM AUTHOR]

An experimental investigation on the strength and ductility of short steel tubes filled with rubberised concrete (RuC), sourced from recycled scrap tyres, is presented in this paper. Firstly, a brief literature review on (i) concrete-filled steel tubes (CFST) and (ii) mechanical characterisation of rubberised concrete is presented. Then, the experimental investigation is described and test results are shown and discussed, namely, the assessment of (i) RuC and steel mechanical properties and (ii) RuCFST column structural properties. The influence of various parameters, such as the cross-section shape (square, rectangular, circular), steel grade, and concrete mix (standard concrete versus RuC), on the short column strength and ductility is analysed and discussed. Eurocode 4 is considered (i) to determine the strength of the tested columns and, in particular, (ii) to assess its applicability to RuCFST columns based on a comparison with the experimental results. The main conclusion of this research is that RuCFST short columns present higher ductility than those made of standard concrete, even though they also show lower strength. This improved ductility is noticeable in columns with circular sections, rather than in square and rectangular sections. From a practical viewpoint, this could be a major benefit for structures in seismic areas where energy dissipation is needed. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive experimental and numerical study of the global stability of stainless steel circular hollow section (CHS) structural members subjected to combined axial load and bending moment. The experimental investigation, which was carried out on two grade 1.4301 austenitic stainless steel cross-section sizes (CHS 60.5 × 2.8 and CHS 76.3 × 3), included material coupon tests, initial geometric measurements, two column tests, and ten beam–column tests. The test results were employed in a parallel numerical simulation programme for the validation of finite element (FE) models, by means of which a series of parametric studies were carried out to extend the available results over a wider range of cross-section sizes, member lengths and loading combinations. The experimentally and numerically derived data were used to assess the structural performance of CHS beam–columns and to determine the accuracy of the current design provisions given in the European code, American specification, Australian/New Zealand standard, and other recent proposed approaches. Generally, all the existing design methods were shown to yield a high degree of scatter in the prediction of beam–column strength, with both conservative and over-predicted capacities. The scatter was attributed mainly to inaccurate predictions of the column buckling and bending end points of the design beam–column interaction curves (i.e. member strengths under pure compression and pure bending, respectively) and inaccurate interaction factors. The development of improved provisions for the design of stainless steel circular hollow section beam–columns is currently underway. [ABSTRACT FROM AUTHOR]

A significant number of macroscopic constitutive models is available to simulate the behaviour of unreinforced masonry (URM) in compression, but they produce different predictions of sectional response to eccentric compressive loading. In this paper, nonlinear moment–curvature analysis of rectangular URM cross sections is presented to explore the influence of alternative constitutive models and ultimate limit state assumptions in terms of post-peak strength degradation and strain ductility. Theoretical moment–curvature diagrams are quantitatively compared to experimental data at multiple levels of load eccentricity through goodness-of-fit measures. Different constitutive models are found to produce a good simulation of experimental moment–curvature behaviour, depending on whether experimental data are disaggregated in terms of masonry type or not. Moment–curvature diagrams are derived by keeping constant either the magnitude or the eccentricity of axial load. Finally, the effects of tensile properties and model error of theoretical moment–curvature diagrams are assessed. [ABSTRACT FROM AUTHOR]

A significant number of existing reinforced concrete building structures were designed and built before 1970, prior to the enforcement of modern seismic design codes. The response of these structures when subjected to cyclic loads, such as that induced by earthquakes, is strongly influenced by the bond properties between the reinforcing bars and the surrounding concrete. This paper describes the results of a testing campaign composed of seven unidirectional cyclic tests and one monotonic test performed on full-scale columns built with plain bars, without adequate reinforcement detailing for seismic demands. An additional unidirectional cyclic test was carried out on a specimen with deformed bars for reference. The influence of bond properties, a cold joint at the base, lapping of longitudinal reinforcing bars, amount of reinforcing steel, cross-section dimensions and imposed loading history (monotonic or cyclic) is discussed. Finally, a correction coefficient to the expressions of EC8-3 for the calculation of ultimate rotation capacity of columns with plain reinforcing bars is proposed. [ABSTRACT FROM AUTHOR]

Abstract: This paper develops techniques for application of spectral method in dynamics of structures, particularly bridges under the moving loading. Spectral method is formulated in terms of matrix operators capable of discretizing and combining Kirchhoff–Love plates and Bernoulli beams. The boundary conditions have been imposed using Lagrange multipliers so combinations of Dirichlet and Neumann conditions could be dealt with. The proposed method allows a bridge to be represented as a 3D structure with realistic cross-section (ribs, box girders, etc.). Moving loading can be any realistic model of a vehicle such as standard European three-axle road vehicle with 9 dynamic degrees of freedom. Vehicle behaviour is described with an additional system of differential equations that has to be solved together with a partial differential equation of the bridge model. Two different formulations and the corresponding methods of solution are presented: (i) formulation suitable for direct solution and (ii) formulation suitable for semi-direct (staggered) solution. The proposed approach based upon the spectral matrix operators is sufficiently general to be suitable for dealing with strong form of any structure analysis problem. Example of dynamic analysis of a real bridge in Croatia illustrates the proposed method. [Copyright &y& Elsevier]

Abstract: The present work describes an analytical and graphical procedure to evaluate stresses in reinforced concrete sections to be used in the verification of the serviceability limit states. The stress limitation imposed in EC2 [1], as well as, the calculation of crack widths and deflections make mandatory the evaluation of concrete and steel stresses at critical cross sections subjected to the service combinations of actions. The serviceability limit states verification is actually very important in the case of higher strength classes of concrete and steel, where it may be determinative in the design. The stress distribution in reinforced and pre-stressed concrete cross-sections is not continuous, due to the fact that the tensile stress of concrete in cracking tension zones is disregarded, and only the compression concrete is considered. The problem formulation is possible by the use of Heaviside functions, similarly to what is made for ultimate limit design of cross-sections in Barros et al. [2]. The integration process through Heaviside functions and MAPLE software is original, it permits a closed form solution to solve the problem, and to obtain abacus relevant for design. This paper presents the theoretical developments and examples of the design abacus for singly and doubly reinforced rectangular and T sections. [Copyright &y& Elsevier]

Abstract: The mechanical behaviour of unbonded post-tensioned (UPT) shear walls of high-strength CAlcium SIlicate ELement masonry with Thin-Layer Mortar (CASIEL-TLM masonry) was investigated experimentally and numerically. Eight walls were tested with the following key variables: unit type, prestress level and cross-sectional shape (rectangular or T-shaped with interlocking of web and flange). An extensive measurement scheme was adopted that allowed derivation of average curvatures and strains in the bottom region of the wall in addition to wall displacements. Since UPT masonry is characterised by the absence of local compatibility between masonry and the UPT tendons, a numerical model for quasi-static, monotonic push-over analysis was developed that provides an iterative solution for the global interaction between masonry and UPT tendons. A common masonry stress–strain diagram was adopted in the numerical model. A peculiarity of CASIEL-TLM masonry is the kicker course, which reduces the stiffness of the bottom region of the shear wall. This layer was modelled with no-tension, linear-elastic behaviour and a reduced stiffness. Nevertheless, the model underestimates the experimental deformations of the rectangular shear walls, while the strength is in reasonable agreement. The walls with T-shaped cross-section failed prematurely by shear of the web-flange interface, resulting in diagonal splitting cracks in the interlocking units. This paper deals with the experimental results of UPT CASIEL-TLM masonry shear walls with rectangular and T-shaped cross-section and with the numerical modelling of the overturning behaviour of UPT shear walls with rectangular cross-section. [Copyright &y& Elsevier]

Abstract: This paper presents the findings from an experimental study of nine H-shaped steel beam-columns with large width-thickness ratios subjected to combined constant axial force and cyclic bending about the weak-axis. Considering different categories of cross-sections, various width-thickness ratios for the flange and web of the specimens are selected, and a reliable structural testing system is developed. The test results show that local buckling dominates the failure mechanism of all the specimens without overall buckling being observed. For bending about the weak-axis, the H-shaped steel members exhibit favorable plastic deformability, and it is concluded that the classification rules in the current design specifications for H-sections are unsuitable for weak-axis bending scenarios. In addition, it is found that the effects of the flange/web width-thickness ratios as well as the axial force ratios on the hysteretic behavior are strongly dependent on each other, and thus should be considered in an interactive way. [Copyright &y& Elsevier]

Abstract: This paper presents an experimental research work to evaluate prestress losses in pretensioned prestressed concrete. An experimental program including variables such as concrete mix design, specimen cross-section size and concrete age at the prestress transfer was carried out. Several pretensioned prestressed concrete prismatic specimens were made and tested using the ECADA+ test method, based on measuring prestressing reinforcement force. In addition, specimens were instrumented to obtain the longitudinal concrete strains profiles at any time. Measurements from both techniques were taken over 1year. Measured prestress losses included elastic shortening losses and time-dependent losses due to concrete shrinkage and creep. A coefficient to account for the relationship between the prestress losses from the measured prestressing forces and the actual prestress losses from concrete compressive strains is proposed. The experimental results were compared with the predicted prestress losses using methods from several codes. [Copyright &y& Elsevier]

Abstract: In this paper a boundary element method is developed for the inelastic analysis of Euler–Bernoulli beams of simply or multiply connected constant cross-section having at least one axis of symmetry, resting on two-parameter tensionless elastoplastic foundation. The beam is subjected to arbitrarily distributed or concentrated vertical loading along its length, while its edges are subjected to the most general boundary conditions. A displacement based formulation is developed and inelastic redistribution is modeled through a distributed plasticity model exploiting material constitutive laws and numerical integration over the cross-sections. An incremental–iterative solution strategy along with an efficient iterative process are employed, while the arising boundary value problem is solved employing the boundary element method. Numerical results are worked out to illustrate the method, demonstrate its efficiency and wherever possible its accuracy. [Copyright &y& Elsevier]

Abstract: This paper describes one approach to the analysis and design of prestressed concrete precast road bridges, with double U-shaped cross-section and isostatic spans. The procedure used to solve the combinatorial problem is a variant of simulated annealing with a neighborhood move based on the mutation operator from the genetic algorithms (SAMO). This algorithm is applied to the economic cost of these structures at different stages of manufacturing, transportation and construction. The problem involved 59 discrete design variables for the geometry of the beam and the slab, materials in the two elements, as well as active and passive reinforcement. The parametric study showed a good correlation for the cost, geometric and reinforcement characteristics with the span length, which can be useful for the day-to-day design of PC precast bridges. A cost sensitivity analysis first indicates that a maximum 20% rise in steel costs leads to an 11.82% increase in the cost, while a 20% rise in concrete costs increases the cost up to 4.20%, namely 2.8 times less. The analysis also indicated that the characteristics of the cost-optimized bridges are somewhat influenced by different economic scenarios for steel and concrete costs. Finally, there is a growth in the volume of concrete when the steel cost rises; surprisingly, the variation in the volume of concrete is almost insensitive to its rising price. [Copyright &y& Elsevier]

Abstract: This paper deals with steady state thermoelastic problems in beam structures using the variational asymptotic method. First, we simplify the original three-dimensional heat conduction problem into a two-dimensional thermal cross-sectional analysis along with an optional one-dimensional heat conduction analysis. The refinements up to the second order of the initial curvatures and twist are captured in the model. Having obtained the temperature field, we then construct a generalized Timoshenko model for the one-way coupled thermoelastic analysis. Several examples will be used to demonstrate the application and performance of the present model. The results will be compared with three-dimensional thermoelastic analysis using ANSYS. [Copyright &y& Elsevier]

Abstract: This paper presents an efficient inelastic and large deflection analysis of space frames using spread of plasticity method. New accurate formulae are proposed to describe the plastic strength surface for steel wide-flange cross sections under axial force and biaxial bending moments. Moreover, empirical formulae are developed to predict the tangent modulus for cross sections under the combined forces. The tangent modulus formulae are extended to evaluate the secant stiffness that is used for internal force recovering. The formulae are derived for steel sections considering the residual stresses as recommended by European Convention for Construction Steelwork (ECCS). A finite element program based on stiffness matrix method is prepared to predict the inelastic large deflection behavior of space frames using the derived formulae. The finite element model exhibits good correlations when compared with the fiber model results as well as previous accurate models. The analysis results indicate that the new model is accurate and computational efficient. [Copyright &y& Elsevier]

Abstract: An experimental and numerical study of the shear response of lean duplex stainless steel plate girders is described in this paper. A total of nine welded plate girders were tested. Lean duplex stainless steel, which is a low nickel variety of the material, has approximately twice the strength of the common austenitic grades and at approximately half the initial cost. It also possesses good corrosion resistance and high temperature properties, as well as adequate weldability and fracture toughness. Two web panel aspect ratios and a range of web slendernesses were considered. The results from the experiments, including the full load-deformation histories and failure models are reported. A numerical investigation was carried out in parallel with the testing. The models were first validated against the experimental results after which parametric studies were performed to generate data for a wider range of cross-sections. The generated experimental and numerical data were used to assess the shear resistance design equations given in Eurocode 3: Part 1.4. The current design provisions were shown to be safely applicable to lean duplex stainless steel, though improved guidance is sought in further ongoing research. [Copyright &y& Elsevier]

Abstract: This paper proposes a framework for the assessment of structural safety of ships under different operational conditions by evaluating performance indicators such as reliability and redundancy. Flexural failure mode for several ship cross-sections is investigated. Reliability and redundancy are based upon the evaluation of the flexural capacities associated with the ultimate hull failure and the failure of the first stiffened panel within a selected cross-section. Furthermore, aging effects due to corrosion phenomena are investigated. Polar representations of reliability and redundancy are obtained for different encountered sea states, ship speeds and headings, covering a large spectrum of operational conditions. Load effects due to waves are computed based on strip theory, while flexural capacity is simulated using Latin Hypercube sampling. The proposed approach is applied to a Joint High Speed Sealift. [Copyright &y& Elsevier]

Abstract: The paper presents the static analysis of non-planar asymmetric shear wall structures with connecting and stiffening beams. The stiff beams incorporated at the various levels of coupled shear walls improve the stiffness of the structural system of tall buildings. The analysis is based on a variant of the continuous connection method for three-dimensional shear wall structures having stepwise changes in cross-section. In the continuous approach the connecting beams are replaced by equivalent continuous connections. The shear walls are considered as thin-walled beams of open section. The differential equation systems for shear wall structure segments of the constant cross-section are uncoupled by orthogonal eigenvectors. The results obtained by the presented method have been compared with those obtained experimentally and analytically, given in literature, and a good match has been observed. The proposed method is efficient and can be very useful, particularly, at the preliminary design stage. [Copyright &y& Elsevier]

Abstract: This paper deals with buckling aspects of the design of stepped columns in mill buildings. These columns are generally loaded axially at the top and at the section where the cross section changes. These loads usually act eccentrically and thus produce column moments. Additional bending from lateral loads also has to be accounted for. Starting from these considerations, a geometrically nonlinear model for buckling behaviour analysis is proposed and formulated using the differential equations of equilibrium. The concept of equivalent (or effective) lengths of the two column segments is successfully applied. Tables to determine effective length factors are provided for a range of the following parameters: end fixities, ratio of the end axial load to the intermediate axial load, the ratio of the length and moment of inertia of the upper segment to the lower segment and the splice mechanical properties. This is followed by a study of the imperfection sensitivity to the linearly evaluated critical load. A discussion on the variation of the load carrying capacity with the level of eccentricity and lateral load acting at the step on a practical column is also presented. The findings suggest that upper and lower segments are treated as separate beam-columns. Some implications for design, in the form of interaction equations, are deduced from the presented analysis. [Copyright &y& Elsevier]

Abstract: Precast segmental construction technique is an excellent candidate for economic rapid bridge construction in highly congested urban environments and environmentally sensitive regions. This paper presents three dimensional nonlinear finite element models using ABAQUS⧹Standard for evaluating the behavior of segmental precast post-tensioned piers under lateral loads. The piers were constructed by stacking precast concrete filled fiber reinforced polymer tube segments one on top of the other and then connecting the assembly structurally with vertical post-tensioning tendons passing through ducts located in the precast segments. A stress–strain relationship for confined concrete was used to model the concrete. The post-tensioning tendons were modeled with beam elements. The model was able to predict the backbone curves for two piers subjected to cyclic loads. A parametric study indicated that increasing the applied post-tensioning force increases nominal strength. Finally, the model showed that the pier aspect ratio, cross sectional diameter size, pier size, and confinement have significant effects on the performance of the investigated piers. [Copyright &y& Elsevier]

Abstract: Arches are frequently used in large span structures like bridges and roofs. Although these structural elements may be prone to various instability phenomena, stocky arches or slender arches with sufficient lateral bracing fail due to plastic collapse instead of in-plane buckling or out-of-plane buckling. The plastic collapse load can be obtained through limit load analyses, making full use of the plastic capacity of the cross-section and possible redistribution of internal forces after formation of the first hinge. This paper describes an analytical approach to obtain the plastic collapse load of circular steel arches subjected to vertical loading. The upper-bound theorem, lower-bound theorem and kinematic admissibility rules of plastic theory were employed to arrive at a plastic collapse load. Reduction of the full plastic moment capacity of the arch cross-section due to the presence of compressive forces was accounted for. An iterative procedure was found necessary to obtain the plastic collapse load since a non-linear relationship was observed between the acting loads and the reduced plastic moment capacity. Finite element analyses were performed to verify analytical results. Good agreement between the suggested iterative procedure and finite element computations was found. Design graphs were developed based on the iterative procedure. [Copyright &y& Elsevier]

Abstract: Lateral instability of elliptical hollow section (EHS) members in bending is studied in this paper. Eight laterally unrestrained EHS beams, with a constant cross-sectional aspect ratio of two, were tested in three-point bending. The test set-up, material properties, section geometry, residual stress measurements and full load-deformation responses of the test specimens are reported herein. To supplement the experimental data, numerical models were also developed and validated against the test results. Parametric studies were then performed, to assess the influence of cross-sectional aspect ratio and member slenderness on lateral stability. Based on the assembled structural performance data, lateral torsional buckling curves for elliptical hollow section beams have been developed and statistically verified. Limiting lengths below which lateral torsional buckling (LTB) need not be considered have also been proposed. [Copyright &y& Elsevier]

Abstract: This paper presents a study on the structural behavior of 15 reinforced concrete beams. The beams were 3m long and the rectangular cross section measured 0.20×0.30m2. They were subjected to two concentrated forces, applied at a third of the span until the failure occurred. The beams had different amounts of longitudinal and transverse reinforcement and were divided into five series. Their strength, deformation and type of failure were analyzed. The main results are presented and discussed in terms of load-displacement, moment–curvature, ductility factor and plastic rotation capacity. In the light of the results it was concluded that beams with high tensile reinforcement ratios suffer premature failure due to the buckling of the compressive bars. These results indicate the importance of the stirrups spacing in RC beams. The influence of the tensile reinforcement ratio and the transverse reinforcement on the plastic rotation capacity and on the general beam behavior was analyzed. This experimental study made it possible to define maximum values for ρ and minimum values for A sw/s to ensure a certain structural energy dissipation capacity. [Copyright &y& Elsevier]

Abstract: In this paper a general solution to the geometrically nonlinear analysis of plates stiffened by arbitrarily placed parallel beams of arbitrary doubly symmetric cross section, subjected to arbitrary loading is presented. The plate–beam structure is assumed to undergo moderate large deflections and the nonlinear analysis is carried out by retaining nonlinear terms in the kinematical relations. According to the proposed model, the stiffening beams are isolated from the plate by sections in the lower outer surface of the plate, while the arising tractions in all directions at the fictitious interfaces are taken into account. These tractions are integrated with respect to each half of the interface width, yielding two interface lines along which the loading of the beams as well as the additional loading of the plate is defined. Their unknown distribution is established by applying continuity conditions at the interfaces, in all directions. The utilization of two interface lines for each beam enables the nonuniform distribution of the interface transverse shear forces and the nonuniform torsional response of the beams to be taken into account. Six boundary value problems are formulated and solved using the Analog Equation Method (AEM), a BEM based method. Application of the boundary element technique leads to a system of nonlinear and coupled algebraic equations which is solved using iterative numerical methods. The adopted model permits the evaluation of the shear forces at the interfaces in both directions, the knowledge of which is very important in the design of prefabricated ribbed plates. [Copyright &y& Elsevier]

Abstract: The use of high strength concrete (HSC) in columns has become more frequent since a substantial reduction of the cross-section is obtained, meaning that slenderness increases for the same axial load and length, producing higher second order effects. However, the experimental tests in the literature of reinforced concrete columns subjected to axial load and lateral force focus on shear span ratios, according to Eurocode 2 (2004), clause 5.6.3., lower than 6.5. This gap in the literature limits technological development for the construction of these structural elements. This paper presents 44 experimental tests on reinforced concrete columns subjected to constant axial load and monotonic lateral force. The aim of this is to gain greater knowledge of the types of elements which will also be of use in calibrating the numerical models and validating the simplified methods. The test parameters are strength of concrete (normal- and high-strength concrete), shear span ratio, axial load level and longitudinal and transversal reinforcement ratios. The strength and deformation of the columns were studied, and an analysis of the simplified methods from Eurocode 2 (2004) and ACI-318 (2008) concluded that both are very conservative. [Copyright &y& Elsevier]

Abstract: In variable humidity conditions, wood absorbs or desorbs moisture from the air. Unless the change in humidity is very slow, this will develop moisture gradients in the wood sections. These gradients will develop stresses due to constrained swelling or shrinkage strains. These stresses are named moisture-induced stresses. The present paper investigates the main parameters affecting such moisture-induced stresses, including the type of climate, the size of the timber cross-section, and the type of protective coating. A first attempt to identify moisture-induced stresses in different European climatic regions was made. For each climatic region, relative humidity and temperature histories were identified, and characteristic and mean values of yearly and daily variations were calculated. Using a finite element model implemented in Abaqus, the moisture content and stress distribution were computed on different timber cross-sections exposed to the climatic regions and protected with different types of coating. A Fickian moisture transfer model was used to compute the moisture distribution, and a mechanical model for time-dependent behaviour of wood was implemented to calculate the corresponding stress distribution. The variation of moisture was found to result in stresses of magnitudes that would probably cause cracking of wood in the perimeter of any uncoated cross-section size. The use of a protective coating, however, reduced considerably the moisture-induced stresses, and can be regarded as an effective protective measure to avoid cracking due to humidity variations. Considering European climates, Northern climates were found to result in higher surface tensile stresses than Southern climates. [Copyright &y& Elsevier]

Abstract: Frame elements may be subjected to significant bending moments about cross-sectional minor axis such as space frame elements and struts that buckle about minor axes. In some cases such as columns with compound cross-sections, the major bending moment acts about minor axes of cross-sectional components. The present paper proposes a simplified model for predicting the second order inelastic behavior of steel frame elements under axial compression force and bending moment about minor axis. New formulae are proposed to describe the plastic strength surface for steel I- and H-shaped cross-sections under axial force and bending moment about minor axis. Moreover, empirical formulae are developed to predict the tangent modulus for those cross-sections. The tangent modulus formulae are extended to evaluate the secant stiffness that is used for internal force recovery. The formulae are derived for steel sections considering the residual stresses as recommended by the European Convention for Construction Steelwork (ECCS). A finite element program is prepared to predict the inelastic second order behavior of plane frames using the derived formulae. The derived model exhibits good correlations when compared with the fiber model results. The analysis results indicate that the new model is accurate, furthermore it saves a lot of calculation time that may be consumed by iterations on the cross-sectional level. [Copyright &y& Elsevier]

Abstract: This paper examines representations of a beam with periodically variable cross-sections. First, the rotational equivalence of a beam with two periodical steps to a uniform beam is considered when a constant bending moment is applied along the lengths of the two beams. The representation is then extended to a beam with several different steps and then to a beam with a variable cross-section. Variable bending moments are also taken into account in the equivalent representation. Equivalent representations based upon the same maximum deflection and fundamental natural frequency are derived. If a beam consists of several periodically variable units and the bending moment in each unit is considered to be constant, the various equivalent criteria can be unified. Detailed finite element analysis (FEA) shows that the plane-deformation assumptions no longer hold in the transition regions between adjacent steps. The transition area is defined using a straight line with an angle determined by curve-fitting and the results are provided in a tabular form considering all related parameters. A comparison of the maximum displacement and fundamental natural frequency shows good agreement for a number of beams with periodically variable cross-sections and their equivalent uniform beams. The study demonstrates that the equivalent representation of a beam with periodical variable cross-sections is accurate and simple to apply to engineering practice. [Copyright &y& Elsevier]

Abstract: In this paper, an accurate and efficient numerical procedure is proposed for the nonlinear inelastic time-history analysis of suspension bridges subjected to earthquake excitations. The proposed procedure includes both geometric and material nonlinearities. The geometric nonlinearities of tower and girder members are taken into account by the use of stability functions, while the geometric nonlinearities of cable members are considered using exact analytical expressions of an elastic catenary. The gradual yielding along the member length and over the cross-section is included using a tangent modulus concept and a refined plastic hinge model. A computer program utilizing Newmark’s average acceleration algorithm with Newton–Raphson iteration is developed. The obtained results are compared with those generated using the commercial package SAP2000 to illustrate the accuracy and computational efficiency of the proposed procedure. [ABSTRACT FROM AUTHOR]

Abstract: Strength interaction diagrams are common tools for reinforced concrete (RC) cross-section analysis and design. They usually relate the ultimate values of the bending moments and axial force, allowing quick assessment of a cross-section’s strength. Under fire action, however, substantial changes occur on the behavior of the cross-section, and these diagrams become strongly dependent on the temperature field, which introduces thermal strains and modifies the stress–strain relationships. The purpose of this paper is to present an algorithm for the construction of strength interaction diagrams for arbitrary-shaped RC sections subjected to fire action. The diagrams are obtained by a stepwise variation of the deformed configuration, under assumptions of conventional ultimate strain values for concrete and steel. The procedure is illustrated by the construction of interaction diagrams for some RC sections subjected to different temperature distributions. [ABSTRACT FROM AUTHOR]

Abstract: Multilayered beams consist of an association of beams of different materials and cross-sections, linked by deformable connections which allow for relative horizontal slip between the layers, and are present in several engineering applications. The purpose of this paper is to study the behavior of the general case of multilayered composite beams with interlayer slip, under Euler–Bernoulli as well as Timoshenko beam theory assumptions. Analytical formulations are presented for the linear case, along with a new description based solely on the interlayer slips, which allows easy determination of closed-form solutions for statically determinate beams. Numerical examples employing association of beam and zero-thickness interface elements are presented, and their accuracy is verified against the analytical solutions. Slip or curvature locking problems are addressed for the multilayered case. It is found that the association of beam and interface elements provides a simple yet efficient solution for multilayered beam analysis. [Copyright &y& Elsevier]

Abstract: The analysis of lateral response of tower-like structures of circular cross-sections due to vortex excitation is considered in this paper. Calculations are carried out according to own mathematical model of vortex shedding and with utilization of own computer program that is an implementation of the model. Maximum top displacements are compared with results obtained according to several well-known standard models and also with full-scale measurements. [Copyright &y& Elsevier]

Abstract: Reinforced concrete members with circular cross section are used frequently in practice. Despite this fact, only limited research on the shear behaviour of such structural members has been published. Further, code rules and guidelines for shear design of circular concrete members are almost non-existent. Most code rules are based on shear models for rectangular members. The shear behaviour of circular members is, however, quite different from that of rectangular members. The difference is especially pronounced for members containing high shear reinforcement percentages. This paper presents the results of a test series on heavily shear reinforced circular concrete members. The specimens had shear reinforcement percentages up to more than three times the maximum percentage found in existing tests. The test results indicate that it is possible to obtain shear strengths which exceed the upper limit usually imposed on rectangular members. The test results are compared with a recently developed plasticity-based shear model for circular members. Satisfactory agreement was found. Comparisons were also made with calculations using the AASHTO LRFD design code. It was found that the AASHTO LRFD design code gives reasonable results for members with small amounts of shear reinforcement while it underestimates the shear strength for heavily shear reinforced members. [Copyright &y& Elsevier]

• Validation of analysis methods. • Comparison of tessellated and conventional shear walls. • Analyses of tessellated walls with varying edge tile patterns. • Damage definitions and quantification for aiding designers. • Parametric study involving parameters like concrete strength and reinforcement ratio. • A simplified analytical model to estimate the capacity of tessellated shear walls. This paper studies the lateral behavior of a reinforced concrete tessellated structural-architectural (TeSA) shear wall system. TeSA walls are made of prefabricated repetitive tiles and have the ability to localize damage which occurs under extreme loading. A TeSA wall is intended for architectural interest, automated construction, reconfiguration, disassembly, and reuse. This study focuses on TeSA tiles that are topologically interlocking in two directions. Nonlinear finite element analysis is used to study the monotonic pushover behavior of TeSA walls with different edge tile configurations and a comparison is made thereof with a conventional reinforced concrete shear wall. The results indicate that the strength of TeSA walls is not significantly affected by the configuration of edge tiles. Damage progression in tiles and the number of damaged tiles that need to be replaced are also presented at different drift ratios. The study shows that reinforcement ratio substantially affects the wall lateral capacity. Finally, a simplified cross-sectional analysis procedure is proposed to provide a lower and upper bound estimate of the lateral capacity of TeSA walls. [ABSTRACT FROM AUTHOR]

• A database of FRCM-strengthened RC beams and FRCM-concrete joints was collected. • Two methods were proposed to compute the FRCM effective strain from the beam tests. • The FRCM effective strain and debonding strain of direct shear tests were compared. Debonding of fiber-reinforced composites can limit the increase of strength that a reinforced concrete (RC) beam can achieve due to the addition of the external layer of reinforcement provided by the composite. Small-scale direct shear tests can help understand the debonding phenomenon. However, researchers have debated for decades whether the results of direct shear tests can be used to predict the strain level at which the composite would fail in strengthened beams. This paper is the first systematic attempt to address this issue. A database of RC beam flexural tests and of direct shear tests that feature externally bonded polypara-phenylene-benzo-bisoxazole (PBO) fiber-reinforced cementitious matrix (FRCM) composite is compiled. For the beam tests, two methods are employed to determine the strain in the composite at failure due to debonding, referred to herein as the cross-sectional analysis method and the Δ M method, and the results are compared with those of direct shear tests. The relationship between the effective strain in the FRCM when composite action is lost and the debonding strain in direct shear tests is critically discussed taking into account what is prescribed by current design guidelines. The limitations of the cross-sectional analysis method to determine the effective strain are also highlighted. [ABSTRACT FROM AUTHOR]