Load Deflection Research Articles

Mechanical properties of alkali-activated slag based SIFCON incorporating waste steel fibers and waste glass

This experimental study focuses on sustainable slurry infiltrated fiber concretes (SIFCONs) by utilizing alkali-activated ground granulated blast furnace slag (GGBS) and waste fibers. The waste fibers were high-strength steel fibers recovered from scrap tires. Additionally, waste glass was employed as a substitute for commercial sodium silicate activator, contributing to the reutilization of a waste material. Such an approach stands out for its use of various waste materials to achieve a high-performance concrete primarily composed of recycled materials. Literature survey indicate that there are no studies available on concrete primarily composed of waste or recycled materials. In this study, the molarities of the activators were selected as 8 M and 14 M based on a prior research. Due to the fiber geometry and the associated bulking effect, a maximum waste fiber content of 5 % was adopted, with increments of 1 %. Load–deflection curves of the specimens were obtained in the bending test. Various mechanical properties, including compressive strength, splitting tensile strength, flexural strength, and fracture energy, were determined for the mixtures. The mechanical properties of the alkali-activated mixtures were improved compared to those of the reference concretes. Based on the mixture proportions and materials employed, alkali-activated mixtures in the study achieved compressive strengths exceeding 120 MPa and flexural strengths approaching 30 MPa. Furthermore, significant enhancements in fracture energies were observed. The strengths of the mixtures with waste glass, however, were lower compared to the other mixtures. Nonetheless, in summary, the study shows the promising potential of waste steel fibers and waste glass for the production of alkali-activated slag SIFCON. This approach not only enhances cost-effectiveness, sustainability, and mechanical properties but also reflects a significant step towards achieving a concrete composition that relies solely on waste materials.

Effect of test parameters on the punching-shear strength of precast tunnel segments reinforced with GFRP bars

While assessing the load cases is crucial for designing the precast concrete tunnel lining (PCTL) segments, none of the tunnel-specific standards or codes explicitly consider punching-shear loads. This study aimed at determining the structural performance of full-scale precast concrete tunnel segments reinforced with glass fiber-reinforced polymer (GFRP) bars. The segments were constructed with a rhomboidal shape measuring 2100 × 1500 × 250 mm and subjected to point loading on their extrados surfaces until failure. Such loading simulates the geotechnical exposure conditions surrounding tunnels, such as rock expansion. The effects of concrete strength and GFRP flexural reinforcement ratio on the punching behavior were analyzed and are discussed herein. The load–deflection response, failure mode, punching strength, cracking behavior, reinforcement and concrete strain, deformability, and energy absorption were all evaluated in the experiments. The results reveal that increasing both the flexural reinforcement ratio and concrete strength enhanced the punching response and decreased crack width. In addition, using HSC in tunnel segments yielded higher pre-cracking stiffness, punching-shear capacity, and energy absorption. A theoretical investigation involving a comparison between predictions of the FRP-reinforced concrete slab design provisions and experimental results was performed to assess the applicability of the current punching equations for PCTL segments. The equations in the FRP-reinforced concrete codes predicted the punching capacities conservatively, while the researchers’ proposed equations overestimated. Moreover, CAN/CSA S806-12 showed the most accurate prediction of the punching capacity even if the concrete compressive strength exceeded 60 MPa.

A unified shear strength equation for slabs and beams longitudinally reinforced with FRP or steel bars based on simplified cracked elastic properties

At service load conditions, deflections and stresses in reinforced concrete (RC) slabs and beams are typically calculated using the properties of the transformed cracked cross section. For more than eighty years, the depth of compression zone factor k in cracked singly-reinforced rectangular RC sections has been calculated using k=2ρn+ρn2-ρn where ρ is the reinforcement ratio and (n) is the modular ratio. It is shown that in slabs and beams with a wide range of concrete compressive strength fc′ that are reinforced longitudinally with steel or FRP bars, ρn ranges from 0.005 to 0.16. Within this range, k can be accurately calculated using k=0.95ρn0.43 or simply k=ρn0.44. The error between the former equation and the exact equation ranges from –2% to + 3 %. This equation is used to show that the shear strength of concrete vc in the ACI–440.11-22 code for GFRP–reinforced members depends effectively on ρ, fc′ and d, just like the strength of steel–reinforced members in the ACI–318-19 code equation. It is proposed to apply to the factor Er/Esteel1/3 where Er and Esteel are the moduli of elasticity of the FRP and the steel bars respectively to the ACI–318 equation to make it suitable also for FRP–reinforced members. This unifies the equation for the two types of reinforcement and provides a better correlation with the experimental results from 233 FRP–reinforced members available in the literature than the current ACI–440.11 code equations. On the other hand, the transformed cracked moment of inertia Icr can be related solely to ρn and approximated using Icr=0.36ρn0.81bd3 where b and d are the sectional width and effective depth respectively. This equation is used to show that the cracked flexural stiffness is effectively related to the modulus of elasticity and the area of the reinforcing bars raised to the power 0.8, to d2.2 and to modulus of elasticity of the concrete raised to the power 0.2.

External precast concrete nib beam-to-column connection under elevated temperatures: Experimental and finite element analysis

The precast concrete nib is one of the most widely used beam-to-column connections to address the architectural drawback of the ordinary precast concrete corbel. However, precast concrete nib beam-to-column connections are not classified as fully rigid or pin but exhibit semirigid properties. Semirigid connections are at risk of deflection at lower loads and cracking during early fire events. In this study, full-scale fire tests were carried out to determine the thermal and structural behaviour of the external monolithic and precast concrete nib beam-to-column connections subjected to 120 min standard cellulose fires. A finite element simulation using ANSYS validated the experimental results based on the internal temperature distributions, load–deflection curves, and stress visualization. Results show that the tension reinforcement of the concrete nib specimen at high temperature was below the critical temperature of 300 °C during the 120 min of heating, compared to the monolithic specimen, which reached the critical temperature of 300 °C at 105 min. The crack patterns and failure modes of monolithic and precast concrete nib specimens at high temperatures were more visible than at ambient temperature. Based on the ductility factor and Monforton’s fixity factor, the concrete nib specimen at high temperatures was categorized as structures with limited ductility and classified in Zone I (pin connection), respectively. This study concluded that external precast concrete nib beam-to-column connections were more vulnerable at high temperatures than monolithic connections.

Experimental Study of Mechanical Behaviour of an RC Concrete Prepared Using M-Sand along with Chemical Admixtures

Abstract: Concrete plays a predominant role in the construction industry and a large quantum of sand is being utilized for various construction of structure. River sand has become expensive due to excessive cost of transportation from natural sources. Also, large- scale depletion of these sources creates environmental problems. So as to overcome, M- Sand can be an economic alternative to the river sand with respect to its availability, cost and environmental impact M-sand a by-product from the stone crushing unit which is released directly into environment can cause environmental pollution. And can be defined as residue, tailing or other non-voluble waste material after the extraction and processing of rocks to form fine particles. Recycling is the key component of modern waste management system and it reduce the consumption of fresh raw materials, reduce energy usage, reducing the need for conventional waste disposal and to lower greenhouse gas emission. To investigate the mechanical properties as compressive strength “Cubes” of size 150 mm x 150 mm x 150 mm are prepared, the Split tensile strength “cylinder” of size 750mm x 150 mm x 150 mm and also load deflection of beam and column are prepared and investigation should be carried out at a regular interval of 7,14 and 28 days. And also, the dynamic behavior is also studied. This present work is an attempt to use M-sand as a replacement (25%, 50%, 75% & 100%) for River Sand in M-30 Grade concrete mix.

Experimental and theoretical investigation of the structural behavior of reinforced glulam wooden members by NSM steel bars and shear reinforcement CFRP sheet

Abstract Reinforcing the wooden structural members is considered as a challenging matter to overcome the drawbacks of using wood in the construction field. The current investigation, therefore, presents an attempt to evaluate the effectiveness of utilizing steel bars as reinforcements in glulam timber beams using the near-surface-mounted (NSM) technique in conjunction with carbon fiber-reinforced polymer (CFRP) sheet wraps. A series of flexural testing was carried out until failure for both reinforced and unreinforced glulam members in a simple support system. Eleven specimens were examined in two groups to compare them with the control beam. Five reinforced glulam (RG) beams of the first group were reinforced with different schemes at tension and compression zones using the same bar size. The other five specimens of the second group were reinforced with shear reinforcement using fully wrapped strips made of CFRP sheet in addition to the same flexural reinforcement schemes as the first group. Each glulam beam has a span of 1.35 m and a rectangular section sized 85 mm × 175 mm. Based on experimental outcomes, theoretic modeling was provided to estimate the ultimate load capacity and bending rigidity of reinforcing glulam members. Though several theoretical predictions of flexural capacity were overstated when compared to experimental predictions, these disparities were frequently about 10%, confirming that the proposed theoretical model was accurate, and the mean of ultimate loading capacity and deflection between experimental and theoretical results were 1.01 and 1.09, respectively. Experimental results presented show that the RG beams performed much better than the unreinforced reference beams in terms of structural behavior, with improvements in ultimate load capacity ranging from 16 to 49%. On the other hand, the shear reinforcement for RG members slightly improved flexural performance, and the ultimate load capacity increased by 2–7%. Therefore, it was concluded that the NSM techniques using ordinary steel bars were effective ways in strengthening the glulam members in terms of flexural stiffness with increasing ultimate load capacity.

Geometrically Nonlinear Buckling of FG-CNTRC Plates Stiffened by FG-CNTRC Stiffeners Subjected to Combined Loads Using Nonlinear Reddy’s HSDT

The nonlinear buckling and postbuckling of functionally graded carbon nanotube reinforcement composite (FG-CNTRC) plates resting on the nonlinear effect of elastic foundation under combined load including external pressure and axial compression loads with uniformly distributed temperature rises are fully investigated in this paper. The FG-CNTRC plates are reinforced by FG-CNTRC stiffeners and the plate-foundation interaction is modeled using a nonlinear model. The higher-order shear deformation plate theory with the geometrical nonlinearities of von Kármán is applied to establish the basic formulations. Additionally, by using the anisotropic higher-order shear deformation beam theory, a new smeared stiffener technique is successfully developed for FG-CNTRC stiffeners. Galerkin’s method is used to achieve the equilibrium equation system in the nonlinear algebraic forms, and the critical load and postbuckling load–deflection curve expression are explicitly determined. The numerical investigations discuss the influences of FG-CNTRC stiffeners, hardening/softening nonlinear elastic foundation, uniformly distributed temperature rises, geometrical and material features on nonlinear stability of stiffened FG-CNTRC plates.

Model Testing of Rock-Socketed Piles under Combined Vertical–Lateral Loading

Abstract This paper presents the findings from a model experimental setup designed and fabricated for conducting single gravity (1-g) model experiments on model aluminum instrumented piles embedded in synthetic rock subjected to both independent vertical–compressive and lateral loading and combined vertical–compressive and lateral loading. Synthetic rock was prepared based on a mix design that can simulate the strength and modulus of soft rocks. Model tests were carried out on single piles of different socketing lengths (L/D ratios: 6, 9, and 12). Combined loading tests were done such that the resultant of the vertical–compressive and lateral loads was at constant inclinations (30° and 60°). Piles with smooth and rough surfaces were simulated for examining the effect of the pile–rock roughness profile. The vertical load–settlement and the lateral load–deflection response were measured from the tests. The bending behavior of piles under both independent and combined loading was also measured. The deflection profile of the rock-socketed pile was obtained by tracing the tested/failed piles after extracting them. The axial and lateral resistance of the rock-socketed piles are interpreted and discussed. It is observed that the rock-socketed piles behave in a distinctly different manner under combined loading compared with independent loading.

Behavior of hybrid FRP-concrete-steel double-skin tubular beams with ultra-high strength concrete and PBL shear connectors under bending

Hybrid double-skin tubular beams (DSTBs) with the external fiber-reinforced polymer (FRP) tube-annular concrete-inner steel tube configuration have excellent mechanical performance and corrosion resistance, but are prone to slip problems. In this study, perfobond shear connectors (PBLs) are proposed to reduce the slip between infilled concrete and inner steel tube. Moreover, using ultra-high strength concrete (UHSC) as the annular material could further improve the structural performance and magnify the lightweight merit of hybrid DSTBs, while hybrid DSTBs with PBLs and UHSC have not been investigated yet. To this end, three-point bending experiments were conducted to hybrid DSTBs with PBLs and UHSC to study the flexural behavior. The mid-span load–deflection curves revealed a three-branched behavior: (i) a first linear ascending branch up to the first yielding at the extreme tension fiber of inner steel tube; (ii) a transition branch to the peak load with a significant slope deterioration when infilled concrete in the compression side reached the unconfined failure strain; (iii) a post-peak residual branch characterized by progressive load reductions over a number of load plateaus. The adoption of UHSC could significantly delay the plastic hinge formation in inner steel tube, and meanwhile improve the bond with PBLs. Thus, the slips between infilled concrete and inner steel tube were minimal (less than 0.2 mm) for most of the specimens, except for those with foamy sheet insertions between PBLs (at around 1 mm). In the end, the design loads of the hybrid DSTBs were predicted by a sectional analysis with high level of accuracy (average error at 6%).

Nonlinear in-plane thermomechanical stability of shallow sandwich micro-arches including strain gradient tensors

The microstructural-dependent nonlinear in-plane stability characteristics of functionally graded (FG) sandwich shallow micro-arches subjected to a uniformly distributed lateral load in conjunction with a temperature rise are investigated in the current study. In this regard, the third-order shear flexible arch formulations are established within the framework of the modified strain gradient continuum mechanics. The considered sandwich micro-arches are made of nanocomposites reinforced with graphene nanofillers based upon various FG lamination patterns. The Chebyshev–Gauss–Lobatto type of gridding scheme together with the pseudo arc-length continuation technique are employed to employ a numerical solution strategy for tracing the size-dependent lateral load–deflection and lateral load–axial load nonlinear stability plots. It is observed that by adding a rise in the temperature to the applied uniform lateral load, the first bifurcation lateral load enhances, while the second one reduces. Also, it is dedicated that there is a unique value of the applied uniform lateral load corresponding to which the axial resultant load as well as the induced lateral deflection in the micro-arch are the same for all values of the temperature rise. Moreover, it is revealed that by increasing the value of the rise in the temperature, the size dependency in the value of the upper limit lateral load becomes less prominent, while it enhances in the value of the lower limit lateral load.

Damage Assessment of Segmental Concrete Beams with Different Types of Joints and Prestressed External Tendons

Precast segmental beams with prestressed external tendons have become increasingly common in bridge constructions owing to the merits of high-quality control and fast onsite construction with minimum environmental impact. Due to the nonlinear characteristics of the dynamic behavior of these segmental beams associated to the joint opening, the traditional condition monitoring and damage assessment methods based on vibration parameters either in time or frequency domain using the linear theory are unsuitable. To overcome this challenge, this paper proposes a damage assessment method through analyzing nonlinear structural dynamic responses for monitoring the conditions of segmental beams with different joint types and prestressed external tendons. Two damage indices are proposed to identify the occurrence of damage and to qualitatively indicate the damage severity. In the proposed approach, the measured dynamic responses of the segmental concrete beams under hammer impact are first adaptively decomposed into a finite number of mono-components by using variational mode decomposition (VMD) technique. Then, the instantaneous frequencies of the decomposed mono-components from the dynamic responses are obtained by conducting the Hilbert transform. Two damage indicators are defined for the damage assessment and for the identification of the damage location, respectively. Three four-span segmental beams with different types of joints (i.e. dry joints or epoxy joints) and prestressing tendon types (i.e. steel and carbon fiber reinforced polymer tendons) were constructed and tested under five loading levels with different damage severities. The feasibility and accuracy of the proposed approach are verified by comparing the identification results with the secant and initial stiffness extracted from the load–deflection curves at different loading levels. The effectiveness of these two damage indicators is also validated with the structural conditions observed in the tests. The results show that the proposed approach can successfully identify damage in segmental concrete beams.

Structural performance of fiber-reinforced SCC beams containing Stalite lightweight aggregates

This study intends to investigate the structural performance of large-scale fiber-reinforced lightweight self-consolidating concrete (LWSCC) as well as lightweight vibrated concrete (LWVC) beams made with Stalite aggregates under flexure loads. A total of fourteen reinforced concrete beam specimens were tested under a four-point bending configuration until failure. Two different binder contents (550–600 kg/m3), two types of lightweight aggregates (coarse and fine Stalite aggregates), two PVA fiber lengths (8–12 mm), and three fraction volumes of fibers (0.3%, 0.5%, and 1%) were considered in this study. The structural performance of the tested beam specimens was assessed in terms of load–deflection response, cracking behavior, energy absorption, displacement ductility, cracking moment, and ultimate flexural strength. This study also investigated the performance of design code provisions in predicting the cracking and ultimate moment capacities of all tested specimens. The results indicated that using shorter PVA fibers seemed to better improve the structural performance of LWSCC beams in terms of deformability, energy absorption, ductility, and ultimate flexural capacity than using longer PVA fibers. Using up to 1% PVA8 fibers in lightweight concrete beams made with Stalite aggregates proved to completely compensate for the drop in ultimate flexural strength that resulted from the use of low-density aggregates and further helped the beams to experience much higher rates of deformation. The results also showed that the model proposed by Henager and Doherty well predicted the ultimate moment capacity of LWSCC/LWVC beams reinforced with PVA fibers.

The effect of using steel fibers reinforced concrete layer in compression zone on the flexural behavior of over‐reinforced concrete beams

AbstractDuctility is one of the most important requirements of RC design besides other requirements such as strength and stiffness. In recent years, concrete beams with a large amount of tensile reinforcement ratio (ρ) have been required in large projects, such as high‐rise buildings and bridges. Using high (ρ) increases the strength and stiffness of the beams and leads to a decrease the ductility. This paper aimed to investigate the effect of using steel fibers reinforced concrete (SFRC) layer in compression zone on the flexural behavior of over‐reinforced concrete beams. Partial replacement of concrete with SFRC layer in compression zone was used to avoid the brittle compression failure of concrete. For this purpose, 12 over‐reinforced concrete beams with a span of 1300 mm and a cross‐section of 120 mm × 180 mm were cast and tested under a three‐point loading. The first beam was used as a reference beam and others as strengthened beams using SFRC layer. The effects of thickness and length of strengthening layer, (ρ), volume fractions of steel fibers, and strengthening methods on flexural performance of tested beams were investigated. The flexural capacity, failure modes, crack patterns, load–deflection relationships, load–strain relationships, ductility index, and toughness were evaluated. The results showed that the suggested technique (SFRC layer in the compression zone) is an effective technique to increase ultimate load, ductility, and toughness by up to 35.72%, 121.01%, and 349.16%, respectively, compared to the reference beam. Furthermore, the failure mode changed from brittle to ductile failure. Also, one of the main advantages of this technique is allows to increase of (ρ) up to 8.55% (4.15ρb) without needing the compressive reinforcement. The results of this study indicate that the using SFRC layer in the compression zone is an appropriate and economical method to provide high flexural capacity and ductility over‐reinforced concrete beams.

Experimental study on flexural behavior of segmental precast large-cantilevered prestressed concrete cap beam

This study investigates the influence of epoxy joint configuration and longitudinal reinforcement continuity at the joints on the mechanical properties of segmental precast assembled large-cantilevered prestressed concrete (PC) cap beams under the co-action of flexural and shear internal forces. Accordingly, a practical project is considered, and five segmental precast-assembled large-cantilevered PC cap beam models as well as a comparative model of a monolithic precast large-cantilevered PC cap beam are designed and produced. The five segmental precast cap beam models were designed with a 1/5 scale ratio, and the joint interfaces were all connected using an epoxy resin binder. Three of these models whose longitudinal reinforcements at the joints were discontinuous utilized a large key tooth, a small key tooth, and corbel joint structures. The other two models whose longitudinal reinforcements at the joints were connected by grouted sleeves adopted large key-tooth and corbel joint configurations. Throughout the static loading test process of these six cap beam models, key results, such as the initial stiffness, cracking load, yield load, ultimate load capacity, concrete strain, deflection, and crack width, were obtained. The experimental results are as follows. The failure process and crack distribution patterns of each precast segmental cap beam model are fundamentally the same as those of the monolithic precast cap beam model. The crack distribution is sparse, cracks are wide, and the failure modes are all due to bending. Additionally, the mechanical properties of the three precast segmental cap beam models with discontinuous longitudinal reinforcement compared with those of the monolithic precast cap beam model were considerably degraded. The initial stiffness, yield load, ultimate load capacity, and ultimate deflection were only 81.4%, 80.4%, 81.1%, and 66.4%, respectively, of those of the monolithic precast cap beam model. Moreover, penetrating cracks formed in the concrete of the tensile zone on both sides of the epoxy joint interfaces during failure. Compared with the segmental precast cap beam models with discontinuous longitudinal reinforcement, the initial stiffness, yield load, ultimate load capacity, and ultimate deflection of the segmental precast cap beam models with continuous longitudinal reinforcement significantly improved. The mechanical properties of the latter were similar to those of the monolithic precast concrete cap beam model. Based on the experimental results, effective technical measures (such as grouted sleeves) were proposed to connect the longitudinal reinforcement at the joints. This ensured that the static performance of the segmental precast-assembled large-cantilevered PC cap beam was similar to that of the monolithic precast cap beam.

Mechanical properties, flexural behaviour, and ductility characteristics of fibre-reinforced geopolymer mortar

This study aims to explore the potential of ambient-cured geopolymer as a substitute for ordinary Portland cement (OPC)-based mortar. However, due to their brittle nature, geopolymer materials require reinforcement to enhance ductility. To address this, an experimental program was conducted to investigate the effects of adding polypropylene (PP) and micro steel (MS) fibers to fiber-reinforced geopolymer mortar (FRGM) at volume fractions of 0%, 0.5%, 1%, and 1.5%. The ternary blended geopolymer mortar consisting of fly ash (FA), and ground granular blast furnace slag (GGBS), along with a novel pozzolan called eco-processed pozzolan (EPP) was investigated. The present study assessed the hardened properties of the FRGM, including compressive strength, splitting tensile strength, modulus of elasticity (MoE), ultrasonic pulse velocity (UPV), and the compressive strength of the material when exposed to elevated temperatures. The aim of this study was also to investigate the load–deflection response in terms of deflection, load, flexural strength, and toughening mechanisms; and also, the bonding between the fibers and the mortar matrix was examined using field emission scanning electron microscopy (FESEM). The results indicated that including 0.5% PP fibers and up to 1.5% MS fibers marginally improved compressive strength and MoE. The corresponding increments in splitting tensile strengths were 5% and 134%, respectively. The addition of fibers improved the fracture parameters of the FRGM. The inclusion of both MS and PP fibers significantly enhanced post-cracking flexural and toughness energy. At deflection L/150, MS fiber mixes exhibited 4–5 times higher toughness energy than PP fiber mixes, and also its evidently observed in the FESEM micrographs. The incorporation of 1.5% fiber volume to non-fibrous mix resulted in an improvement of 43.2 N.m. and 10.1 N.m. in toughness (T150) for MS and PP mixes, respectively. At an elevated temperature of 600 °C, the FRGM specimens gained a massive reduction in compressive strength, with the maximum result being at 87% for 1.5PP and 71% for 0.5MS. Overall, the MS fiber-reinforced geopolymer mixes exhibited superior performance as compared to PP fibers.

Influence of concrete and unbonded ratio on RC beams

Hybrid aggregates, comprising normal-weight and lightweight aggregates, offer an effective means to enhance the physical and mechanical properties of concrete. However, the comprehensive effect of hybrid aggregate concrete on the flexural performance of reinforced concrete (RC) beams remains largely unexplored. In this study, utilizing LC30 lightweight concrete, LC40 gravel lightweight concrete, hybrid aggregate lightweight concrete, and hybrid aggregate concrete with reduced ceramsite content as matrix materials, RC ordinary beams and RC bond-slip beams with dimensions of 150 mm × 300 mm × 2400 mm were meticulously designed and fabricated. Employing a four-point bending test, the effects of the concrete matrix, the unbonded ratio, and the reinforcement ratio of the bottom longitudinal rebar on the flexural behavior of the two types of beams were scrutinized. Furthermore, the load–deflection and load–slip responses were subjected to numerical simulation using the finite element method. The findings demonstrate that hybrid aggregates exert a substantial influence on adjusting the dry apparent density, strength, and elastic modulus of concrete to align with design specifications. While the physical and mechanical characteristics of both beam types are primarily governed by the reinforcement ratio and unbonded ratio, the concrete matrix, despite its distinct properties, exhibits minimal effect on these attributes. Nevertheless, it significantly affects beam stiffness and the relative slip between the rebar and the concrete matrix. Both beam categories adhere to the plane section assumption and reveal that optimal collaborative performance between the rebar and concrete matrix occurs at a bottom longitudinal reinforcement ratio of 1%, albeit diminishing with escalating unbonded ratios. The failure progression of both beam types can be categorized into three stages: elastic phase, crack propagation phase, and compressive failure phase. The process of crack advancement, the load–deflection profile, and the load–slip behavior of the beams manifest similarities, albeit subject to variations attributable to the concrete matrix, bottom longitudinal reinforcement ratio, and unbonded ratio. The Menetrey–Willam constitutive model effectively replicates the load–deflection and load–slip characteristics of both beam types. However, its simulation precision is influenced by the friction coefficient existing between the rebar and the concrete matrix. Notably, this friction coefficient undergoes alteration in consonance with the concrete failure process, thereby reflecting the gradual degradation of bonding performance between the rebar and the concrete matrix.

Shear capacity of traditional joints between walls made of AAC masonry units

AbstractThe article presents the synthesis of the results of tests performed on unreinforced joints of walls made of autoclaved aerated concrete. The shape of the research element and the testing set up were innovatively designed based on the own research, literature review and numerical analyses. The article discusses the morphology of cracks and the mechanism of failure as well as the load–deflection relationship of the unreinforced joints made with traditional masonry bond. The individual work phases of the joints were specified and the rigidity of the joint was calculated. Using standardized procedures, parameters for the design of the joints were given. The obtained results encourage further analyses on the detailing of the joints and applications of new methods in the construction of the joints.

Post-fire properties of beam-slab specimens with different restraints on interior beams

This study investigated the influence of the vertical restraint of the interior beam and columns on the post-fire mechanical behaviours of four beam-slab specimens. Two vertical restraints and interior beams with and without a rigid vertical restraint were investigated. In addition, a numerical model was developed to analyse the load–deflection curves and membrane actions of the beam-slab specimens after exposure to fire. A plane equation and deflection parameter were proposed to predict the yield-line and ultimate loads of fire-damaged beam-slab specimens with different vertical restraints. The results revealed that, compared with the vertical restraint of the interior beam, the restraint of the columns has a greater effect on the ultimate loads of the beam-slab specimens after exposure to fire. Compared with the experimental and numerical results, the proposed elliptic equation method can be used to analyse the ultimate loads and membrane action distribution of the beam-slab specimens with different restraints of the interior beams.

Numerical and analytical investigations on the flexural behaviours of composite beams of inverted-T steel section and ultra-high-performance concrete (UHPC) slab

This study numerically and analytically investigates the flexural performance of a new form of steel–concrete composite beam, where an inverted-T section is connected to ultra-high-performance concrete (UHPC) slab that serves as the compression chord. Such arrangement eliminates the necessity for the top flange and absorbs the compressive stresses when the beam is under construction. Thus, the aim of this study is to develop a comprehensive finite element (FE) model for the proposed inverted-T steel-UHPC composite beam in ABAQUS by considering both geometric and material nonlinearities. The developed FE model was validated against the existing experimental results, and afterwards the validated FE model was employed to conduct an extensive parametric study. In the parametric study, the effects of different design parameters including slab thickness, concrete compressive strength, stud spacing, stud diameter, effective width of slab and web penetration depth were investigated in terms of the load–deflection, bond-slip, and damage patterns. Furthermore, the load–deflection and load-slip behaviors of the proposed beam were compared with the conventional steel–concrete composite beam. Finally, an analytical procedure was developed to determine the flexural resistance of the inverted-T steel-UHPC composite beam. The results of this study will pave the way toward a practical application that is expected to decrease the construction time and cost.

Phenomenological comparison between the flexural performance of steel- and CFRP-reinforced concrete elements

In recent decades, FRP reinforcement has received increasing attention in engineering research of reinforced concrete composites due to its advantages over steel reinforcement, such as corrosion resistance and high strength. Due to brittle failure and high strength-to-stiffness ratio of the FRP reinforcement, the flexural behavior of FRP-reinforced beams exhibits a qualitative and quantitative difference compared to conventional steel-reinforced elements. In particular, understanding and improving material utilization is crucial to reduce material consumption and maximize design efficiency in view of the increasing environmental concerns. In this paper, a phenomenological comparison of the flexural behavior and material utilization for various design configurations for steel- and CFRP-reinforced elements is presented. The investigations include different concrete grades, FRP reinforcement properties, cross-section shapes, and hybrid steel–FRP reinforcement cross-sections. In order to deliver a comprehensive perspective to design efficiency in practical context, serviceability deflection limit has been derived for FRP reinforced elements and integrated into the evaluation scheme. Additionally, a general modeling framework for the investigation of the moment–curvature and load–deflection response of steel- and FRP-reinforced beams has been developed supporting the presented studies. The modeling approach is based on a numerical evaluation of the cross-section equilibrium and it supports different material laws as well as arbitrary cross-section shapes and reinforcement layouts. The obtained results show fundamental differences between the bending capacity and material utilization of steel- and FRP-reinforced elements, which can stimulate the development of resource efficient designs. A deeper understanding of the phenomenology based on the present studies can streamline the current research on innovative design concepts for FRP-reinforced concrete elements with optimal utilization of these high-performance materials.