Beam Depth Research Articles

Inelastic cyclic response of RBS connections with jumbo sections

This paper examines the cyclic performance of reduced beam section (RBS) moment connections incorporating larger member sizes than those allowed in the current seismic provisions for prequalified steel connections, through experimentally validated three-dimensional nonlinear numerical assessments. Validations of the adopted nonlinear finite element procedures are carried out against experimental results from two test series, including four full-scale RBS connections comprising large structural members, outside the prequalification limits. After gaining confidence in the ability of the numerical models to predict closely the full inelastic response and failure modes, parametric investigations are undertaken. Particular attention is given to assessing the influence of the RBS-to-column capacity ratio as well as the RBS geometry and location on the overall response. The numerical results and test observations provide a detailed insight into the structural behavior, including strength, ductility, and failure modes of large RBS connections. It is shown that connections which consider sections beyond the code limits, by up to two times the weight or beam depth limits, developed a stable inelastic response characterized by beam flexural yielding and inelastic local buckling. However, connections with very large beam sections, up to three-times the typically prescribed limits, exhibited significant hardening resulting in severe demands at the welds, hence increasing susceptibility to weld fracture and propagation through the column. The findings from this study point to the need, in jumbo sections with thick flanges, for a deeper RBS cut than currently specified in design, to about 66% of the total beam width. This modification would be required to promote a response governed by extensive yielding at the RBS while reducing the excessive strain demands at the beam-to-column welds. Moreover, for connections incorporating relatively deep columns, it is shown that more stringent design requirements need to be followed, combined with appropriate bracing outside the RBS, to avoid out-of-plane rotation.

Size effect of large high strength concrete beams with or without shear reinforcement

This paper presents a research programme conducted on a total of seven large high strength concrete (HSC) beams, up to 1800 mm in depth and 13400 mm in span, with and without shear reinforcement in the web. This study investigates experimentally the effects of aggregate size, shear reinforcement ratio, and effective depth on shear strength of large HSC beams. In addition, the test data are adopted for verification of design provisions in ACI 318–14, ACI 318–19 and EN 1992–1-1. It is experimentally shown that reduction in ultimate shear strength was observed with increasing beam depth, regardless of the maximum aggregate size and web reinforcement ratio. A larger beam depth led to a more extensive development of flexural and shear cracks, as well as a greater beam stiffness. Besides, the use of smaller aggregates results in a higher ultimate strength (in MPa) for the beams. Shear equations from ACI 318–14 overestimated shear strengths of the large HSC beams without web reinforcement, while ACI 318–19 and EN 1992–1-1 predictions were more conservative by accounting for the size effect term. It is also shown that the existing codes of practice could not account for the effect of aggregate size when determining shear strength. Additionally, predictions by all the three codes for the HSC beams with minimum shear reinforcement were generally conservative.

Effect of polyethylene terephthalate fibres on the structural performance of reinforced concrete beams with openings in the shear region

The provision of transverse openings in the shear region of beams to allow passage of services reduces the cracking and ultimate load capacities of the beams and increases deflection under the openings, especially when the size of the opening exceeds 25 % of the overall beam depth. Strengthening of the pre-planned opening regions by use of special steel reinforcements causes reinforcement congestion and difficulties in compaction, calling for alternative ways of strengthening beams with openings. In this study, concrete material was modified by the use of Polyethylene Terephthalate (PET) fibres produced from waste plastic bottles to improve the tensile properties and hence reduce the cracking around the openings and improve the overall performance of the beams. To evaluate the performance of PET fibres in beams with openings, eight (8) reinforced concrete beams with and without fibres of dimensions (150 × 250 × 2000 mm) were cast with varying opening sizes. The horizontal position of the openings was fixed at 300 mm from the support while the vertical position was maintained at the mid-depth of all beams. This performance was evaluated in terms of ultimate and first cracking loads, mid-span deflections, ductility, crack patterns and failure modes, and strain behavior. Test data showed that incorporating PET fibres in beams with openings resulted in a slight increase in ultimate load of 4.1 % and 5.82 % for 0.25 h and 0.35 h beam opening sizes respectively, beyond which the strength was reduced by 9.57 % for beams with 0.45 h opening size, where h was the overall depth of the beam. The first cracking loads increased by 44.12 %, 48.48 %, and 9.38 % for 0.25 h, 0.35 h, and 0.45 h opening sizes, respectively. In addition, a slight improvement in the ductility of PET fibre beams for all opening sizes was observed. The PET fibre beams exhibited a slight change in the mode of failure from dominant shear failure to combined shear and flexure failure characterized by multiple cracks in the flexure region with minimal spacing. An increase in the concrete compressive and tensile strains accompanied by a reduction in concrete and steel shear strains was observed because of the tension stiffening effects of the fibres. The incorporation of PET fibres, therefore, showed a slight improvement in the ultimate performance of beams with 0.25 h and 0.35 h opening size, with no improvement for the control beam and 0.45 h opening sized beam. However, a significant improvement in the serviceability performance for all PET reinforced beams was observed.

Analytical approach and design method for evaluation of compressive arch action of precast concrete beams

This paper proposes an analytical approach to predict compressive arch action (CAA) of precast reinforced concrete (PC) beams subjected to middle column removal scenario (MCRS). A beam-column joint with non-seismic detailing is employed in the prototype PC structures, which is a typical joint widely applied in low seismic-risk countries. However, under MCRS, a weaker sagging moment resistance of the precast interface near the removed middle column casts doubts on its structural performance. Based on particular details of the PC beams, the analytical approach is proposed to consider the influences of a potential plastic hinge at the PC interface, various precast interface locations, special precast reinforcing details and horizontal restraint conditions on the mobilisation of CAA. Furthermore, an easy-to-apply design method is developed by assuming linear relationships between bending moment, neutral axis depth and compression force of the PC beam. Reliability of the analytical approach and the design method is verified through comparisons between predictions and FEM simulations of typical two-span PC sub-assemblages with various design details. The comparison study suggests that both the analytical approach and design method can accurately predict the CAA capacity and corresponding displacement, as well as the maximum compression force and bending moment at PC beam ends. Finally, a parametric study is carried out to shed light on the effects of different precast interface locations and various common design details on CAA peak resistance. It is found that when the distance (L3) between the precast interface and the beam end interface does not exceed a threshold value (L3_c), increasing L3 can significantly enhance CAA capacity. However, when L3 exceeds L3_c, CAA cannot be further enhanced due to transformation of CAA mechanism. It also finds that the threshold value L3_c is highly influenced by reinforcement details, span-over-depth ratio and horizontal stiffness of the beam.

Verification of Uniformity of Dosimetric Characteristics of Couch Tops in Proton Radiation Therapy

In proton therapy the couches used for patient positioning and alignment can affect the uncertainty in the dose distribution from the applied proton beam. In order to limit the additional uncertainty of the proton range, it is necessary to know the determined water equivalent thickness (WET) of the couch top and carefully reflect it in the calculations of the dosimetry planning system. The method presented in this article is based on the difference in the measured depth of the proton beam detected by the multilayer ionization chamber with the beam passing through the couch top and without passing through it.
 A range shifter (proton beam modifier) installed in the nozzle with the known WET for evaluating couch tops before commissioning was used in this research work. A nozzle is a proton beam delivery system consisting of quadrupole magnets, ionization chambers and an X-ray tube. CT scans were also acquired to evaluate the internal homogeneity of the test couch tops.
 Several kVue couch inserts Proton one (Qfix Systems, Avondale, PA) were evaluated in this study. The results show that the inserts are largely interchangeable for this type of design and the use of the range shifter during treatment, using gantry angles with the proton beam passing through the couch top, does not affect its WET, adding a deflection of approximately 0.1 mm. It was also determined that the reproducibility of the WET determination method has a deviation less than ±0.03 mm. In conclusion, the described above method of couch top testing before commissioning in proton therapy can also be applied to other patient immobilization systems.

Nonlinear finite element analysis of high and ultra-high strength concrete beams reinforced with FRP bars

ABSTRACT A finite element (FE) model is carried out to study the bending behavior of concrete beams constructed of high and ultra-high strength concrete (HSC/UHSC) under three-point bending. The simulated beams are reinforced with longitudinal reinforcement bars from fiber reinforced polymer (FRP) material. The ABAQUS FE software is used in the modeling. The FE model was calibrated using the experimental data of the specimens carried out by M.W. Goldston et al. (2017). Twenty-eight validated FE models were performed to study the effects of concrete compressive strength (high and ultra-high), type of FRP longitudinal bars (AFRP, BFRP, CFRP and GFRP), main FRP reinforcement ratio (0.74%, 1.16% and 1.67%), compression FRP reinforcement ratio (As’ %; 25%, 40%, 100%), and both of beam width and depth (b and d). From the results; it is found that the concrete strength has a small effect on the ultimate capacity. However, the deflection is higher for beams with lesser strength. For all the cases, CFRP reinforced beams showed higher capacity and lesser ductility, while GFRP reinforced beams showed lesser capacity and higher ductility. As’ ratio has insignificant effect on load capacity, but it can improve deflection; it is recommended that As’ did not exceed 40% from AFRP. The beam width has insignificant effect on carrying capacity, but it decreases the corresponding deflection, while increasing the beam depth led to increase the maximum load and decrease the corresponding deflection. Comparable error is generally obtained when using the both equations of Issa and Issa (2017) and ACI440.1 (2015).

Optical design and higher-order aberrations with the superconducting gantry based on limited ramping fields

One of the major challenges in proton therapy is the cost and scale of the treatment facility, which depends mainly on the dimensions of the gantry. A potential method that promises to make the gantry lighter and more compact is superconducting magnet technology. However, the rapid ramping requirements during energy modulation are the primary reason for magnet quenching. To alleviate these restrictions, we propose a superconducting bending section consisting of a TBA lattice for a gantry optical design. With only three magnetic field settings needed to deliver 70–200 MeV proton beams, it achieves ±10% large momentum acceptance owing to its significant dispersion function suppression capabilities. Another feature that contributes to reducing the footprint is the installation of a degrader on the proposed gantry, allowing the degraded beam to be guided directly to the isocenter without being filtered by the Energy Selection System. For verifying the feasibility of the concept, we assess the possibility of beam scraping in the beam path and beam spot distortion at the isocenter. These efforts are accomplished by modeling realistic field distributions with ANSYS Maxwell and then performing 7th-order transfer mapping through COSY Infinity. Regarding the influence of broad energy spread on beam depth dose distribution, TOPAS is used to simulate and compare the integrated depth dose for various therapeutic energies.

Offshore subsurface characterization enabled by fiber-optic distributed acoustic sensing (DAS): An East China Sea 3D VSP survey example

Recent advances in distributed acoustic sensing (DAS) technology have allowed more intense measurements of subsurface and environment events, providing improved geohazard monitoring and subsurface characterization. This study discussed the subsurface evaluation enabled by the DAS-vertical seismic profiling (DAS-VSP) system in the East China Sea, China. Taking advantage of a continuous recording of the vibrational wavefields through the strain deformation of the fiber deployed along the borehole, DAS-VSP is considered an emerging and promising alternative borehole acquisition method. It provides a wider-spectrum range of recordings in a cheaper, denser, and more continuous tense compared to conventional geophones. We explored the 3D DAS-VSP signal processing and imaging strategy. Based on a set of 3D DAS-VSP data of exceptional quality, this study reviewed the common processing challenges and practical solutions for de-noise, de-ghosting, de-multiple, and wavefield separation arising from the DAS acquisition mechanism in the offshore VSP scenario. High-quality down-going multiples were separated and imaged using the pre-stack Gaussian beam depth migration in addition to the primary reflection wavefield, providing significant additional illumination to support the subsurface evaluation. The current results validated the efficiency of the DAS-VSP survey and encouraged better geological interpretation.

Experimental Study on Flexural Bearing Characteristics of Ceramsite Concrete Beams after Creep at Different Curing Ages

Ceramsite concrete is increasingly used for structural applications due to its lightweight, high-strength, and high-temperature resistance advantages. However, research into the postcreep properties of ceramsite concrete has yet to keep pace with other areas. Therefore, this paper aims to investigate the flexural bearing properties of ceramsite concrete beams after creep and make recommendations for future research. To study the flexural load-bearing performance of ceramsite concrete beams after creep, a comparison test was carried out on four ceramsite concrete beams subjected to 200 d creep loading and four beams subjected to static load without creep loading for four curing ages. The results showed that, at first, the deformation capacity of the ceramsite concrete beams would increase after creep and the toughness and energy absorption capacity would also strengthen. Secondly, the creep could improve the ultimate bearing capacity of the ceramsite concrete beams. It was an approximate 10% increase after 200 d creep. Then, the stiffness, toughness, and ultimate bearing capacity of the ceramsite concrete beams would increase gradually with the increase of the curing age after the creep. In addition, the ultimate bearing capacity of the ceramsite concrete beams increased gradually with the increase of the curing age. The growth rate was faster in the early stage, slower after 120 d, and slower and more stable after 228 d. Finally, creep could cause the maximum crack width and depth of the ceramsite concrete beams decreased and the number of cracks would grow with the curing age. The conclusions obtained in the study provide a theoretical basis for the design of light aggregate structures for creep.

Análise de efeito de escala nos mecanismos complementares de resistência ao cisalhamento e sua supressão por reforço transversal - contribuições para a NBR 6118

Abstract Size effects are known to be relevant in the shear transfer mechanisms of quasi-brittle materials like concrete. Bažant proposed an asymptotic approximation between plasticity theory and Linear Elastic Fracture Mechanics (LEFM), showing a proportionality of concrete nominal resistance with d - 1 / 2, where d is beam depth. Recently, the long-standing shear transfer mechanism expressions of ACI 318:2014 have been updated (ACI 318:2019), with introduction of a size effect factor. In Brazil, recent publications identified non-conservative trends in predictions of ABNT NBR 6118:2014 for larger beam depths; yet, the Brazilian code never considered size effects because they are suppressed by transverse reinforcement. Considering this background, in this manuscript we make a comprehensive analysis of NBR 6118:2014 shear strength predictions using as a reference the papers of ACI-ASCE DatStb 445-D database. The results exhibit strong tendencies in the model error regarding longitudinal reinforcement and effective depth for beams without transversal reinforcement. A two-step analysis is made herein to describe model errors: first, a nonlinear regression for longitudinal reinforcement is made; second, a linear regression is made for size effect. The reliability analysis corroborates that model error may be reduced by introducing size effect and longitudinal reinforcement factors. Next, for beams with transversal reinforcement, smoother tendencies regarding beam depth are noted, indicating a size effect suppression for the beams depths available in the database. However, as the analysis shows that the higher beam depths concentrate most of the results with unconservative model errors, further studies are necessary to accurately describe how transversal reinforcement suppress the size effect.

Análise das tendências nos mecanismos complementares de resistência ao cisalhamento de vigas de concreto armado

abstract: The study of shear failure in concrete beams is one of the subjects growing in importance due to both the recent reformulations, and increasingly higher cross-section depths used. For instance, the recent updates in the ACI 318 (2019) shows the need to incorporate the size effect in the design of reinforced concrete elements. In this study, the same database adopted by the ACI-ASCE Committee DAfStb 445-D has been used to calculate shear strength, with and without the consideration of size effect, i.e., the design prescribed by ACI 318 (2014), ACI 318 (2019), Frosch et al. (2017), and the ABNT NBR 6118 (2014). Later these predictions are compared with test results. A dispersion analysis has outlined the trends regarding compressive strength, span to depth ratio, longitudinal reinforcement ratio and beam depth. Every variable was discussed per interval, delineating the causes related to the observable trends. Regarding the most prominent influences (effective depth and longitudinal reinforcement ratio), the approaches considering them directly through factors had provided results with no appreciable trends, with lower coefficients of variation (COV) and substantially more conservative for higher cross-section depths. As the Brazilian code does not consider both, a correction factors, determined by a two-step regression analysis on these parameters to adjust this design, are briefly introduced.

Meso-scale modelling of size effect on shear behavior of Basalt fiber reinforced concrete deep beams

The work aims to examine the size effect on shear failure of deep concrete beams with Basalt Fiber Reinforced Polymer (BFRP) bars. A mesoscale numerical model for the deep concrete beam with BFRP bars was built to explicitly model the shear failure, considering concrete heterogeneity and concrete/bars interaction. The mesoscale simulation approach was firstly verified against the available test observations. It was then utilized to study the shear failure of geometrical-similar concrete deep beams having different structural sizes with BFRP bars and steel bars. The influence of beam depth, stirrup ratio and reinforcement type (i.e., steel bars and BFRP bars) on the shear failure and the corresponding size effect of concrete deep beams was explored. The simulation results indicate that: 1) the failure modes of concrete deep beams with BFRP bars and steel bars are basically similar, and they all exhibit noticeable size effect; 2) stirrups (i.e., steel bars and BFRP bars) can hinder the development of diagonal cracks within concrete, and thus weaken the size effect in shear strength; 3) the shear failure in beams with BFRP bars presents more substantial size effect than that of beams with steel bars; 4) the calculation models of shear capacity in the international codes do not apply to concrete deep beams with BFRP bars. Moreover, it is found that the size effect law developed previously can also be suitable for the shear failure of concrete deep beams with BFRP bars.

Size effect on bending strength of glued laminated timber predicted by a numerical simulation concept including discrete cracking

The dimensions, particularly the depths, of glued laminated timber (GLT) beams are continuously increasing to realize, e.g., wide-span hall constructions or flexible office buildings. However, experimental investigations of large beams are unavailable because of the tremendous effort involved. Numerical simulation campaigns represent an alternative, but their results are heavily influenced by the modeling strategy, and therefore, a different influence of the beam depths on the bending strength was obtained. To predict this influence, also called size effect, we carried out a simulation program covering 8840 GLT beams ranging from 165 mm to 3300 mm in depth, using advanced modeling concepts including discrete cracking and plasticity.We observed a decreasing characteristic bending strength with increasing beam depths and an almost constant mean modulus of elasticity for both considered strength classes. Additionally, the influence of the beam length on the bending strength is analyzed, and it is shown that this influence can be described reasonably well with a simple analytical model based on Weibull’s strength theory. In conclusion, the effective material behavior of GLT is affected by its dimensions. For large beams, this influence is difficult to obtain experimentally; however, numerical simulation campaigns seem to be a promising way to accomplish this.

On the perturbation effect and LET dependence of beam quality correction factors in carbon ion beams.

In a recent study, we reported beam quality correction factors, fQ , in carbon ion beams using Monte Carlo (MC) methods for a cylindrical and a parallel-plate ionization chamber (IC). A non-negligible perturbation effect was observed; however, the magnitude of the perturbation correction due to the specific IC subcomponents was not included. Furthermore, the stopping power data presented in the International Commission on Radiation Units and Measurements (ICRU) report 73 were used, whereas the latest stopping power data have been reported in the ICRU report 90. The aim of this study was to extend our previous work by computing fQ correction factors using the ICRU 90 stopping power data and by reporting IC-specific perturbation correction factors. Possible energy or linear energy transfer (LET) dependence of the fQ correction factor was investigated by simulating both pristine beams and spread-out Bragg peaks (SOBPs). The TOol for PArticle Simulation (TOPAS)/GEANT4 MC code was used in this study. A 30 × 30 × 50 cm3 water phantom was simulated with a uniform 10 × 10 cm2 parallel beam incident on the surface. A Farmer-type cylindrical IC (Exradin A12) and two parallel-plate ICs (Exradin P11 and A11) were simulated in TOPAS using the manufacturer-provided geometrical drawings. The fQ correction factor was calculated in pristine carbon ion beams in the 150-450 MeV/u energy range at 2 cm depth and in the middle of the flat region of four SOBPs. The kQ correction factor was calculated by simulating the fQo correction factor in a 60 Co beam at 5 cm depth. The perturbation correction factors due to the presence of the individual IC subcomponents, such as the displacement effect in the air cavity, collecting electrode, chamber wall, and chamber stem, were calculated at 2 cm depth for monoenergetic beams only. Additionally, the mean dose-averaged and track-averaged LET was calculated at the depths at which the fQ was calculated. The ICRU 90 fQ correction factors were reported. The pdis correction factor was found to be significant for the cylindrical IC with magnitudes up to 1.70%. The individual perturbation corrections for the parallel-plate ICs were <1.0% except for the A11 pcel correction at the lowest energy. The fQ correction for the P11 IC exhibited an energy dependence of >1.00% and displayed differences up to 0.87% between pristine beams and SOBPs. Conversely, the fQ for A11 and A12 displayed a minimal energy dependence of <0.50%. The energy dependence was found to manifest in the LET dependence for the P11 IC. A statistically significant LET dependence was found only for the P11 IC in pristine beams only with a magnitude of <1.10%. The perturbation and kQ correction factor should be calculated for the specific IC to be used in carbon ion beam reference dosimetry as a function of beam quality.

Fracture model for predicting tensile strength and fracture toughness of concrete under different loading rates

For the sake of safety evaluation of concrete structures under dynamic loading conditions, the rate dependences of concrete fracture parameters are necessary to be elucidated rationally first. Therefore, the aim of this study is to develop a fracture model for determining the size-independent tensile strength (ft), the fracture toughness (KIC) and the fracture energy (GF) under different loading rates. The fracture mechanism was analyzed comprehensively using three-point bending tests on concrete beams with varied depths (h) and ratios of the initial crack length to the beam depth (a0/h). As the loading rate increases, the number of fractured coarse aggregates is increased, and the shape of the load–displacement curve around the maximum fracture load (Fmax) becomes sharper. Subsequently, a fracture model was proposed to predict the size-independent parameters ft, KIC and GF by incorporating the average aggregate size (davg) and a discrete coefficient (β) to indicate material heterogeneity and discontinuity, respectively. The critical effective crack length (Δac) was discretized and quantified as davg multiplied by β. Closed-form solutions of ft, KIC and GF were obtained using Fmax based on the boundary effect model. ft, KIC and GF can be explicitly predicted after determining Fmax from the fracture tests, and were generally irrelevant to h and a0/h under individual loading rates, indicating their size-independence. The scatters in the ft, KIC and GF values were determined using a statistical analysis. The rate dependences of the fracture parameters were clarified quantitatively through elucidating the variations in ft, KIC and GF with respect to the loading rate. Moreover, the predicted fracture parameters based on the proposed model were insensitive to the possible variations of davg and β. This study brings a new insight into the fracture behaviors of concrete under different loading rates and provides scientific guidance for the disaster prevention of concrete structures.

Parametric study and design method on unequal depth beams to corner column joints with H-damper

The paper presents the parametric studies and design method of unequal depth H beams-HSS steel column corner joints with H-dampers. According to corresponding experimental studies, nineteen numerical models were created by ABAQUS and their reliability was validated by comparative tests. The design methods and corresponding calculation of H-dampers with three perforated shapes (diamond, ellipse, and vertical) are exhibited. The primary analyzed variables were beam depth ratio (Dbs/Dbw), H-damper types, limb breadth (B), and limb length (lf) of H-dampers. Then, the bearing capacities and initial stiffness of beams and bearing capacities and energy dissipation in H-dampers were studied through parametric analysis. The results indicated that T-connectors and H-dampers could elevate the bearing capacity and initial stiffness of shallow beams. H-dampers exhibited better energy dissipation performance. Besides, web-perforated forms of dampers affected the beams and dampers. Wider limb breadth and shorter limb length enhanced the bearing capacity and initial stiffness of beams, and reduced energy dissipation of H-dampers.

Displacement in Deep Propped Cantilever Beam Subjected to Semi-elliptical Load

A fifth order shear deformation theory considering transverse shear deformation effect is presented for displacement in propped cantilever beam. The considered displacement field accounts for non-linear variation corresponding to depth of beam. Governing equations and boundary conditions of the theory are obtained using the standard of virtual work. Numerical results for static deflection analysis for aspect ratio (length to depth) 2 to 50 for isotropic beam is obtained. The results of present theory are in close agreement with those of higher order shear deformation theories.

Nonlinear Fe Model for Shear Strengthening of Simply Supported RC Beams with FRP DE Bars

Deep embedment (DE) is emerging as a potential and effective shear strengthening approach for existing reinforced concrete (RC) structures. A two-dimensional nonlinear finite element (NLFE) model for simply supported RC T-beams strengthened in shear with embedded carbon fibre reinforced polymer (CFRP) and steel bars is presented in this study. VecTor2, version 4.2, was used to create a two-dimensional NLFE model. To validate the nonlinear FE models, three sets of six simply supported RC T-beams from Breveglieri et al. (2015) are employedEach set consists of two beams with vertical and inclined (45) DE bars. Set one strengthens the beams with steel DE bars without vertical steel stirrups in the shear span. In the shear span, the beams of Sets two and three are reinforced with CFRP DE bars with vertical steel stirrups @180 mm c/c and @300 mm c/c, respectively. The above-mentioned NLFE model is validated by comparing experimental and predicted results for failure load, deflection, and failure mode. For both experimental and simulated beams, the fracture pattern is diagonal, and the failure mode is shear failure. The overall mean predicted/experimental loads at failure and deflection at failure ratios are 1.09 and 1.00, respectively, with corresponding standard deviations of 0.03 and 0.04. Following the validation of the proposed NLFE model's correctness, numerical parametric tests are conducted to determine the influence of concrete compressive strength and effective depth of RC T-beams on shear capacity of simply supported RC T-beams. The parametric analysis findings reveal that enhancing the cylinder compressive strength increases the predicted failure load while increasing the effective beam depth decreases it

Shear behavior of I-section steel with circular web opening and novel reinforcement

For reinforcement of circular web opening in I-section steel beams, half-ring plates of novel configuration were proposed considering the economy and structural performance. To verify the proposed method, cyclic loading tests were conducted for cantilever beams with a single web opening and low shear-span ratio. The test parameters were opening diameter-to-beam depth ratio and degree of reinforcement. The test results showed that the shear behavior of I-section steel was significantly affected by web opening of standard and small diameters (= 50% and 33% of the beam depth, respectively). On the other hand, properly designed ring plates strengthened the perforated beams to exhibit the plastic capacity of solid I-section, restraining the double-curvature flexural mode of web opening (i.e., the Vierendeel mechanism). The proposed ring plates were effective not only in enhancing the flexure-shear strength of the perforated beams, but also in ensuring large inelastic deformation, irrespective of design parameters. The test results, such as the overall load-displacement relationships and buckling modes, were successfully captured by finite element analysis using Abaqus. An existing analytical model for the flexure-shear interaction capacity of the circular web opening was modified to account for the proposed reinforcement method. The predictions conservatively estimated the test strengths.

Progressive collapse resistance of reinforced concrete beam-column connection under fire conditions

To reveal the reinforced concrete (RC) structural response under fire-induced progressive collapse scenarios, 3D finite element (FE) models were developed to investigate the effect of high temperatures on the collapse resisting mechanisms of RC beam-column connections. To describe the behavior of RC connections at elevated temperatures, temperature-dependent thermal and mechanical properties of concrete and reinforcing steel were adopted in the 3D FE model. The sequentially coupled thermal–mechanical analysis was performed with the explicit solver in a quasi-static manner. The concrete damaged plasticity (CDP) and ductile damage for metals (DDM) were adopted to better describe the failure of concrete and steel rebar, respectively. The proposed numerical model was validated by experimental data at different temperatures from literature. To understand better the collapse resistance of RC beam-column connections, a new loading scheme was adopted in the developed model. The load capacity of RC connection under fire conditions was investigated analytically and numerically. The effects of top and bottom reinforcement ratios, concrete strength, beam depth and fire severity on the collapse resisting mechanisms were investigated. The regulated chord rotation failure criteria recommended by the U.S. Department of Defense (DoD) were utilized and showed to be conservative on the collapse identification of RC structures under fire conditions.