Behavior Of Beams Research Articles

Strengthening of RC beams defected in shear using external bonded ribs made of aluminum tube sandwich filled with strain hardening cementitious composites

Installing Aluminum Tubes (ATs) filled with Strain Hardening Cementitious Composite (SHCC) on the sides of Reinforced Concrete (RC) beams for shear strengthening has not been studied before. These tests combine the advantages of aluminum material as a new construction material with the superiority of SHCC for shear treatment of RC beams. Additionally, this study is interesting because it provides a thorough assessment of the special composite system's ability to strengthen RC beams—a capability that hasn't been thoroughly investigated in the literature. With a particular emphasis on comprehending how various aluminum tube rib configurations—such as their orientation, length, and number—can affect the efficacy of the strengthening strategy, this investigation aims to evaluate the improvements in shear capacity, failure modes, and deformation behaviors. Conducted under a one-point loading scheme, the research analyzed eight strengthened RC beams alongside a reference beam to determine the impact of AT rib number and configuration on beam behavior under shear stress. Key findings indicate that diagonal AT ribs, optimally aligned with shear forces, significantly enhance shear strength by 19 %-48 %. This configuration effectively controls and limits the spread of shear cracks, with extended rib lengths halting crack propagation at varying extents—up to two-thirds of the shear span. Notably, vertical ribs demonstrated progressive increases in shear strength as the number of ribs increased, with enhancements of 18 %, 35 %, and 52 % for one, two, and three ribs, respectively. Furthermore, SHCC as a filler material played a pivotal role in these enhancements, leading to a 27 % increase in peak load capacity and a 54 % rise in deflection, compared to those without. One, two, and three vertical ribs showed increases in the ductility by 46 %, 143 %, and 222 %, respectively, while diagonal ribs exhibited the most substantial improvements, with one and two ribs increasing ductility by 158 % and 215 %, respectively.

Numerical Simulation of GFRP-reinforced Rectangular Concrete Beams and Proposed Design Expressions

Rebar corrosion, which has emerged as a primary detrimental factor, significantly impacts the structural performance, durability, and overall serviceability of reinforced concrete (RC) structures. In response to this issue, the growing use of GFRP, which offers superior corrosion resistance compared to steel, highlights the need to compare its performance with traditional steel-reinforced beams. To address this need, this study aims to evaluate the flexural behavior of beams reinforced solely with GFRP rebar and assess their structural performance relative to steel-reinforced beams. To achieve this, finite element models of both steel-reinforced and GFRP-reinforced beams were developed using ANSYS software. The analysis focused on load-bearing capacities, displacement characteristics, and crack patterns, and included the calculation of strain energies corresponding to collapse prevention performance limits. Overall, the study concludes that these modifications enhance design guidelines for GFRP-reinforced beams, offering improved practical applications in structural design. Significant findings include the proposed modification to the minimum reinforcement ratio equation in ACI 440.1R-15 for GFRP-reinforced concrete, the introduction of a suggested strain reduction factor for GFRP rebar, and the revision of the effective moment of inertia equation with coefficients of 0.05 and 0.95. These revisions improved the general performance indicator to 1.17, yielding better results compared to other equations in the literature. The study concludes that these modifications enhance design guidelines for GFRP-reinforced beams, offering improved practical applications in structural design.

Experimental study on the shear behaviour of high-strength lightweight concrete beams incorporating graphene oxide

Graphene oxide (GO) has achieved significant progress in the material behaviour of cement-based materials. However, research on its structural behaviour in high-strength lightweight concrete (HSLWC) structures is limited, which restricts its engineering applications. This study focused on investigating the effects of low contents of GO on the shear behaviour of HSLWC beams. A total of four HSLWC beams with GO contents of 0, 0.01, 0.03 and 0.05% (by weight of cement) were designed to observe failure modes, load‒deformation curves, shear capacities, crack behaviour and load‒strain curves under four-point loading by a 300 kN servo loading device. The results revealed that all the beams exhibited shear compression failure. GO improved the shear capacity of the HSLWC beams, and this strengthening effect increased with increase in GO content. When the content of GO was 0.05%, the ultimate load of the beam reached a maximum, which was 39.2% greater than that of the control beam. GO can endow the HSLWC beams with a certain degree of ductility. In addition, a modified JGJ 12-2006 model was proposed to predict the shear capacity of HSLWC beams containing different GO contents on the basis of a comparison of typical models. This study can provide exploratory engineering practice for evaluating and designing GO-reinforced HSLWC structures.

On buckling of compact I-section beams subjected to biaxial bending

This paper aims at providing a new insight into the lateral-torsional buckling behavior of compact I-section steel beams subjected to biaxial bending, without axial force, a subject seldom treated in the literature. This investigation is based on both analytical and numerical results, the latter obtained using a two-node geometrically exact beam finite element developed by one of the authors (Gonçalves, 2019), which has all the required features. Several geometrically non-linear analysis (GNA) types are used to characterize the buckling behavior, namely with geometric imperfections (GNIA), with material non-linearity (GMNA) and combining material non-linearity and imperfections (GMNIA). Different boundary conditions along the two principal planes are allowed and particular attention is paid to cases which involve the same first-order bending moment diagrams but different support schemes. As a consequence, it is shown that the buckling behavior depends not only on the slenderness and the first-order moment diagrams, but also on the supports. On the basis of results obtained concerning the application of the Eurocode 3 provisions for different support conditions, it is shown that unsafe results can be obtained but may be resolved using the recommendations presented in the paper.

Flexural post-cracking performance of macro synthetic fiber reinforced super workable concrete influenced by shrinkage-reducing admixture

Most literature has focused on the effect of shrinkage-reducing admixture (SRA) in shrinkage mitigation resistance of concrete. This study aims to examine the impact of SRA on the efficiency of macro synthetic fibers (MSF) in enhancing the flexural post-cracking behavior of fiber-reinforced super workable concrete (FR-SWC). A comparative analysis of the influence of fiber combinations on the flexural post-cracking behavior of beams is also included. Results showed that a higher dosage of SRA, particularly at 5 % by mass of binder, had a noticeable negative impact on flexural post-cracking performance of beams while exhibiting positive effect on workability and shrinkage reduction. However, incorporating low dosages of SRA (1.25 % by mass of binder) did not have a significant impact on the ability of MSF. This was attributed to the reduction of the MSF-matrix bond strength caused by a significant delay in cement hydration. The characteristics of selected MSF type, including length and surface roughness had a positive effect on the post-cracking performance of FR-SWC, regardless of SRA dosage. The notched beams made with 100 % MSFA outperformed those made with fiber combination of 25 % MSFA and 75 % MSFB. Beams made with 100 % MSFA showed 55 % higher residual flexural tensile strength, 49 % higher equivalent flexural tensile strength, 50 % higher fracture energy, and 35 % higher equivalent flexural strength ratio compared to beams made with fiber combination of 25 % MSFA and 75 % MSFB. Therefore, the negative effect of SRA on the flexural-post cracking behavior can be partial compensated by adjusting MSF content and combinations.

Free vibration of sandwich beams with graphene nanoplatelets reinforced piezoelectric face sheets

Owing to its exceptional physical properties, graphene is considered as an excellent reinforcement for composite materials. However, the existing higher-order models encounter significant hurdles when attempting to accurately predict the natural frequencies of sandwich beams with graphene nanoplatelets reinforced composite (GNPRC) piezoelectric face sheets. If transverse shear deformations are not accurately modeled, the dynamic behavior of piezoelectric sandwich beams will be noticeably influenced by the disparities of material properties at the interfaces of adjacent layers, as well as the inherent electromechanical coupling characteristic. To overcome these challenges, an advanced electro-mechanical coupling theory will be introduced for the vibration analysis of sandwich beams featuring GNPRC piezoelectric face sheets. Compared to previous higher-order models, the proposed beam model introduces an enhanced interlaminar shear stress field incorporating electromechanical properties. This improved stress field can be involved in the equations of motion based on the Hamilton principle, significantly enhancing the precision in analyzing the free vibration behavior of piezoelectric sandwich beams. Furthermore, a simplification of finite element implementation can be achieved by removing the second-order derivatives of in-plane displacements from the transverse shear stress field. Consequently, a C0-type three-node beam element is constructed for the dynamic analysis of sandwich beams with GNPRC piezoelectric face sheets. To validate the performance of the proposed theory, the 3D elasticity solutions and results obtained from alternative theoretical frameworks are used. Numerical results demonstrate that the present model offers superior accuracy over the existing higher-order theories. Additionally, a comprehensive parametric investigation is conducted to explore the influence of key parameters on the free vibration characteristics of piezoelectric sandwich beams.

Finite Element Modeling and Artificial Neural Network Analyses on the Flexural Capacity of Concrete T-Beams Reinforced with Prestressed Carbon Fiber Reinforced Polymer Strands and Non-Prestressed Steel Rebars

The use of carbon fiber reinforced polymer (CFRP) strands as prestressed reinforcement in prestressed concrete (PC) structures offers an effective solution to the corrosion issues associated with prestressed steel strands. In this study, the flexural behavior of PC beams reinforced with prestressed CFRP strands and non-prestressed steel rebars was investigated using finite element modeling (FEM) and artificial neural network (ANN) methods. First, three-dimensional nonlinear FE models were developed. The FE results indicated that the predicted failure mode, load-deflection curve, and ultimate load agreed well with the previous test results. Variations in prestress level, concrete strength, and steel reinforcement ratio shifted the failure mode from concrete crushing to CFRP strand fracture. While the ultimate load generally increased with a higher prestressed level, an excessively high prestress level reduced the ultimate load due to premature fracture of CFRP strands. An increase in concrete strength and steel reinforcement ratio also contributed to a rise in the ultimate load. Subsequently, the verified FE models were utilized to create a database for training the back propagation ANN (BP-ANN) model. The ultimate moments of the experimental specimens were predicted using the trained model. The results showed the correlation coefficients for both the training and test datasets were approximately 0.99, and the maximum error between the predicted and test ultimate moments was around 8%, demonstrating that the BP-ANN method is an effective tool for accurately predicting the ultimate capacity of this type of PC beam.

A numerical investigation of the structural behavior of reinforced concrete beams fully or partially encased with UHPC layers in flexure

Weakness in the structural facilities appears due to design faults, poor construction, usage change, maintenance lack, material defects, and environmental conditions. Therefore, strengthening structures becomes necessary for deteriorated concrete and enhancing aging concrete elements to achieve satisfactory performance perfectly. This study numerically investigated the structural behavior of conventional concrete beams reinforced with Ultra-High Performance Concrete (UHPC) layers on different sides. The arrangement of UHPC layers, bonding method between traditional concrete and UHPC, layer thickness, and reinforcement ratio were examined using Abaqus software. The interface between the UHPC layer and conventional concrete sustains compressive, tensile, and shear stresses, which cause weak resistance to the stresses at the contact surfaces. Therefore, the simulation of contact face in Abaqus needs a proper numerical model relying on practical methods. However, using the bonding models available in Abaqus is crucial for reaching logical results comparable to the practical ones. The practical bonding approaches are highly consequential, such as roughening surfaces by sandblasting to attain a firm connection between the contact surfaces, which permits using a surface-based tie constraint for simulation. Further, epoxy resin conducts as a thin coating between contact surfaces, making it possible to simulate via a cohesive surface. The results proved that increasing the area encased by the UHPC layer improves load capacity further and reduces the deflection at the maximum load. Surrounding the beam on whole sides with a UHPC raises load capacity by 108 % and reduces deflection by 46 %. Adding a UHPC layer to the beam delays crack initiation and reduces their number and spacing. Increasing the UHPC layer thickness or reinforcement ratio enhances the load capacity of the beam at cracking and the ultimate state.

Hybrid CFRP‐GFRP sheets for flexural strengthening of continuous RC beams: Experimentation and analytical modeling

AbstractContinuous reinforced concrete (RC) beams cast in place are commonly used in construction; however, there is a notable gap in the literature regarding the performance of continuous RC beams strengthened with fiber‐reinforced polymer (FRP) sheets. Strengthening RC beams with FRP sheets typically leads to reduced ductility and moment redistribution capacity due to the linear stress–strain behavior of FRP materials compared to non‐strengthened RC beams. Addressing this gap, this study explores the feasibility of enhancing the mechanical properties and ductility of strengthened elements through a hybrid approach, combining carbon‐fiber‐reinforced polymer (CFRP) and glass‐fiber‐reinforced polymer (GFRP) sheets. An experimental program was conducted, retrofitting two continuous two‐span RC beams (250 × 150 × 6000 mm) with hybrid CFRP‐GFRP (HCG) sheets. Concentrated loads were applied at the center of each span, and comprehensive data on strains in FRP sheets, longitudinal reinforcements, and crack propagation patterns were recorded and meticulously analyzed. The outcomes demonstrated that employing HCG sheets for strengthening RC continuous beams significantly improves ductility, load‐carrying capacity, and moment redistribution, surpassing the performance of beams strengthened with either CFRP or GFRP sheets. To ensure accurate predictions of the flexural response, an analytical model was developed and rigorously verified using the experimental results. The model takes into account the strain compatibility condition and provides insights into the behavior of continuous RC beams strengthened with CFRP, GFRP, and HCG sheets. This research contributes valuable knowledge to the understanding of FRP sheet strengthening techniques, emphasizing the efficacy of HCG sheets for achieving enhanced structural performance in continuous RC beams.

Flexural behaviour of normal concrete circular beams strengthened with ECC and stainless steel tubes

The use of laminated fibres for strengthening reinforced concrete beams is challenging owing to bonding and compatibility issues, especially in scenarios where cost effectiveness and long-term performance are important. A novel flexural strengthening technique for normal concrete circular beams (NCCBs) is proposed, using engineered cementitious composites (ECCs) and stainless steel tubes (SSTs). To examine the application of the proposed strengthening method, five NCCBs were fabricated and tested under static loading until failure to investigate the effects of ECC thickness and SST thickness. The test results showed that the strengthening technique greatly improved the failure pattern and the ultimate flexural capacity of the tested NCCBs, and the enhancement increased with an increase in the thickness of the ECC and SST. Using Abaqus software, finite-element models were constructed to simulate the performance of the tested NCCBs. The accuracy of the finite-element modelling was confirmed by comparing the simulations with the experimental results. The validated model was used for a detailed parametric investigation of the effects of the thickness of the ECC and SST on the failure and ultimate bending capacity of the strengthened beams.

Bending Behavior of RC Beams with Regular Web Openings and Non-corroding GFRP Reinforcement

The present study pertains to the flexural behavior of RC beams with openings and non-metallic (GFRP) reinforcement. The main goal of preferring GFRP reinforcement over the conventional steel reinforcement was to safeguard the beams against the reinforcement corrosion. The presence of multiple regular transverse openings throughout the beam length increases the susceptibility of reinforcing bars to corrosion as the larger contact area in these beams with the outside environment increases the ingress of corrosive agents. Within the scope of the study, a total of 8 RC beams, including two reference beams without web openings, were tested under four-point bending. The test parameters were the flexural reinforcement ratio, the presence of short stirrups in the chords, and the presence of diagonal reinforcement spiraling around the openings. Since GFRP stirrups are difficult to bend, each stirrups was formed by connecting four individual FRP bars around the longitudinal bars. The opening circular geometry was adopted to avoid stress concentrations around the sharp corners of opening and to facilitate the placement and fixing of different schemes of reinforcement in the beams. The present tests depicted that the diagonal reinforcement around the openings have considerable contribution to the flexural behavior of RC beams with GFRP reinforcement and with multiple regular transverse openings. The RC beams with openings were able to approach their analytical flexural capacities in the presence of diagonal reinforcement for both moderately and heavily reinforced beam groups. The analytical deflection predictions of GFRP-RC beams with openings showed a good agreement with experimental data.

Effectiveness of shear key on torsional resistance of precast beam: An experimental and numerical investigations

The present study evaluates the behaviour of wet precast beam-to-beam connection under pure torsion through experimental and numerical studies. A wet connection is provided at the central region of the precast beam. Two precast beam elements are connected by welding the overlapped portion of reinforcement bars projecting from each beam element. Furthermore, inward and outward shear keys are provided within the connection region to examine the efficacy of shear keys on the torsional resistance of the precast beam. Also, the behaviour of precast beams with and without shear keys is compared with monolithic beams. Experiments are conducted using a loading frame, designed and fabricated to create a pure torsion effect on the beam specimen under the application of monotonic vertical load. The response of test specimens is evaluated through various parameters such as torque and corresponding twist at different phases of loading, torsional ductility index, crack formation and failure propagation. Experimental studies show that shear keys provided within the connection region effectively contribute to force transfer and enhance torsional resistance of the precast beam by 16 %−24 % as compared to monolithic beam and precast beam without the shear key. A numerical analysis of the precast beam is carried out, and the behaviour of test specimens obtained from experimental studies is compared. The damage pattern and torque-twist behaviour obtained from numerical studies adequately simulate the response of test specimens observed during the experimental study.

Analytical investigation on the rotational behavior of dovetail mortise–tenon joints between beams and columns in traditional Chinese timber frames

We theoretically analyzed the rotational behavior of beam–column dovetail joints in traditional Chinese timber frames in this study. An analytical model of dovetail joints at both the column head and body was designed by clarifying the moment generation mechanism and effect of rotational embedment yielding in timber perpendicular to the grain on the rotational behavior of joints. An asynchronous manifestation of rotational embedment deformation across the column surface, tenon cheeks, and upper and lower surfaces of the tenon head was analyzed, and the corresponding characteristic yield points and consequent reduction in rotational stiffness were derived in the model. The Inayama embedment theory was used to clarify the effect of rotational embedment with varying end lengths on the movement of the joint rotation center and asymmetric moment generated in different rotation directions of the column head joint. The precision of the analytical model was validated through a comparative analysis by involving nine sets of experimental data, for estimating the initial stiffness, post-yield stiffness, and identified yield points. The implications of the parameters, including the initial gap between the tenon and mortise, geometric dimensions of the dovetail tenon, and friction coefficient, were also discussed. Controlling the ratio of the initial gap and tenon height within 0.01 to ensure a certain rotational resistance of dovetail beam–column joints within the collapse limits of traditional timber frames is recommended considering the significant effect of the initial gap on the initial sliding angle and moment reduction.

Effects of openings on postbuckling behavior of large‐size composite C‐beam under bending‐shear coupling load

AbstractProper design and accurate mechanical assessment of composite C‐beam after opening are of great importance in structure engineering. This paper aims to experimentally and analytically investigate the postbuckling response of large‐size C‐beam with web opening under bending‐shear coupling load. New specimen with four different open shapes were designed and tested. Strain gauges and displacement measurements were applied to monitor its buckling behavior, strain field distribution and critical failure load. Four specimens with various openings were loaded until catastrophic failure occurred. Additionally, an analytical model was introduced to predict the residual strength of circular opening. The results indicate that while the presence of an opening significantly decreases the load carrying capacity, it has minimal effect on the bending stiffness. Compared with intact specimen, the initial delamination, buckling and ultimate strength of the circular opening decreases less than those of the rectangular opening. By altering the position of the rectangular opening, improvements can be made in terms of initial delamination resistance and buckling load; however, ultimate strength remains largely unaffected. Reinforcing the edge of an opening further reduces resistance to initial delamination but other two indicators are improved. Overall, from buckling to failure stages, post‐buckling bearing capacity after opening decreases by 40%. Moreover, the shear failure mode is observed during catastrophic failures. And the analysis method employed is relatively conservative.Highlights Ten large size composite C beams are conducted under coupling loads. Deformation, strain distribution and failure mode are presented. Influence of openings on postbuckling behavior of beam is analyzed. An analysis method is employed to predict the residual strength of beam. It could provide valuable insights for assisting in designing beam openings.

Generation of pseudo-nondiffracting symmetrical Layer beams using cylindrical lenses

The pseudo-nondiffracting behavior of optical caustic beams makes them potentially useful in precise component alignment at CERN. This paper introduces an innovative method for generating one and two-dimensional symmetrical Airy-like beams, known as Layer beams, utilizing a specific configuration of plano-convex cylindrical lenses. Simulations and experimental results have validated this method, demonstrating its potential for scalable and cost-effective beam production with tunable properties, making it practical for a wide range of scientific applications.

Shear behaviour of continuous fibre-reinforced lightweight aggregate concrete beams

A series of shear tests on six fibre-reinforced lightweight aggregate concrete (FRLWAC) beams containing both steel and polypropylene fibres are presented in this paper. These beams were designed and cast with different boundary conditions, steel fibre contents, and shear-span-to-depth ratios (a/d). From the test programme, it was found that an addition of 0.5 % of steel fibre by volume significantly improved the shear behaviour of continuous FRLWAC beams and mitigated the concern of low shear resistance associated with lightweight concrete. The addition of steel fibre enhanced the direct strut strength of FRLWAC beams in shear and improved the efficacy of stirrups in transferring shear forces. The test results also suggested that continuity effect prevented sudden and complete loss of load-carrying capacity in FRLWAC beams failing in shear, although it did not significantly increase the shear-carrying capacity. A strut-and-tie model was proposed to predict the shear resistance of continuous FRLWAC beams. The contribution of steel fibre in enhancing the efficacy of compression struts and stirrups was considered in this model. This model was shown to be accurate in predicting the shear resistance of FRLWAC beams and was more accurate and reliable compared to available shear strength prediction provisions in different design codes. It also presents a viable alternative to a three-dimensional finite-element model for predicting the shear resistance of continuous FRLWAC beams.

Experimental, analytical, and numerical investigation on flexural behavior of the gradient UHPC-NC composite beams

To enhance the deformation resistance of concrete beams, the flexural behavior of eight gradient ultra-high performance concrete (UHPC)-normal concrete (NC) composite beams was experimentally studied. The effects of different gradients and fiber types on the deflection of the gradient UHPC-NC composite beams were investigated, and a deflection calculation method for the composite beams was proposed. Finally, numerical simulations were conducted on the basis of the cohesion models. Results indicate that the gradient UHPC design significantly improves both the loading-bearing and deformation capacity of the composite beams. The cracking load of the gradient composite beams with steel fiber-UHPC at the bottom layer is much higher than that of the beams with basalt fiber-UHPC, and the number of cracks in the pure bending section of the beams with steel fiber-UHPC at the bottom layer is remarkably less than that of the beams with basalt fiber-UHPC at the bottom layer. However, their ultimate capacities were comparable, indicating that steel fibers can effectively improve the fracture toughness of UHPC. The predicted deflection of the gradient UHPC-NC composite beams agrees well with the test results, indicating the accuracy of the proposed deflection model. The bearing capacity and deflection obtained from the numerical simulation also align well with the test results.

Behavior of Concrete Beam Encasing Castellated Steel Section with Different Opening Size

This research aims to investigate the behavior of castellated steel sections with varying hole sizes enclosed in a concrete beam. Should two different opening size types (depth 140mm and depth 280mm) be used? When we use two types of shear connectors with full and partial interaction, stud connections integrate the steel and concrete parts. This research demonstrates We examined five simply-supported composite beams under two-point loading conditions. We constructed four examples using castellated steel beams and produced one specimen using standard steel beams as a control. We examine the maximum load support capacity. Examined are the specimens of composite beams' deformations. Among the many characteristics assessed are the castellated beam size of the aperture and the whole and partial composite interactions. According to test results, the sample had a 140mm hexagonal hole. The sample experienced an increase in final load percentages of approximately 11.11%. Compared to the sample featuring a 280mm hexagonal opening size, the mid-deflection and horizontal displacement showed a significant increase. The figures indicate a final load of approximately 18.82% and 16.7%, respectively. Full interaction also revealed a higher ultimate load for the sample with the same aperture. When the sample was fitted with a 140mm hexagonal hole, the percentages increased by approximately 6%. Additionally, the percentage of deflection at midspan and the percentage of horizontal displacement decreased by approximately 16.7% and 26.8%, respectively, compared to the sample with a hexagonal opening size of 280 mm.

Stainless steel I-section beams at elevated temperatures: Lateral–torsional buckling behaviour and design

In this paper, a comprehensive investigation into the structural response and design of stainless steel I-section beams susceptible to lateral–torsional buckling (LTB) at elevated temperatures is carried out. A very large number of stainless steel I-section beams are considered, taking into account various cross-section geometries, beam slendernesses and different stainless steel grades and elevated temperature levels. Extensive structural performance data on the behaviour of stainless steel I-section beams are generated through nonlinear shell finite element modelling. Assessment of the existing LTB design rules for stainless steel I-section beams at elevated temperatures provided in the current version of the European structural steel fire design standard EN 1993-1-2 and its upcoming version prEN 1993-1-2 is presented. New LTB design rules based upon an Ayrton-Perry equation that is able to provide a consistent mechanical appraisal of the LTB behaviour of stainless steel I-section beams in fire are proposed. The accuracy and safety of the proposed new LTB design rules for stainless steel I-section beams are comprehensively verified. It is also shown that the proposed LTB design equations in this paper lead to a considerably higher level of consistency and reliability for the LTB design of stainless steel I-section beams in fire relative to the LTB assessment rules provided in EN 1993-1-2 and prEN 1993-1-2.

Hygro-mechanical analysis of timber-timber composite (TTC) beams in time-dependent environments: A 3D coupled finite element approach

The time-dependent behavior of timber-timber composite beams under constant loads within uncontrolled indoor environmental conditions is examined using a 3D fully coupled hygro-mechanical finite element model. These TTC beams are composed of glued laminated timber (GLT) or laminated veneer lumber (LVL) beams interconnected with cross-laminated timber (CLT) slab panels via coach (lag) screw shear connectors. A 3D hygro-mechanical material model, integrated into finite element software, is validated against a long-term experimental study spanning 735 days. A comprehensive sensitivity analysis is performed, exploring the influence of mesh size, time step, coefficient of hygro-expansion/contraction, and contact properties on the results of coupled finite element simulations. This results in the delineation of input parameters (i.e., mechanical properties of materials and screw-to-timber soft-contact model) that are suitable for practical hygro-mechanical simulations of Radiata Pine LVL, GLT, and European Spruce CLT materials. Smoothed temperature and relative humidity data are employed to enhance the convergence of coupled finite element simulations, especially for extended, long-term numerical simulations. Finally, the coupled finite element models are used to forecast midspan deflections in TTC beams over a prolonged duration, specifically after 4000 days.