Mid-span Deflection Research Articles

Effect of different anchorage schemes on the flexural behavior of RC slabs strengthened with CFRP sheets

This research investigated the behavior of RC slabs subjected to four points loading with five different CFRP sheet numbers (1, 2, 3, 4, 5) and three different anchorage systems (Type 1 used CFRP strips in the transverse direction, Type 2 used galvanized steel end plates without grooving, Type 3 used galvanized steel end plates with grooving). A total of twenty reinforced concrete (RC) solid slabs were cast to fulfill the study objectives. Results showed that the presence of CFRP strips enhanced the slab's ultimate load capacity by 102 %, reduced mid-span deflection by 12 %, also improved energy absorption capacity and stiffness by 36 % and 32 %, respectively. Type 2 anchorage system without grooves and type 3 anchorage system with grooves both used galvanized steel end plates and enhanced the flexural capacity of the slabs by 119 % and 125 %, respectively, also improved the RC slab properties and shifted the failure mode from delamination to a CFRP strips rupture. The introduced anchorage system without grooving was found to be an efficient and easily applied technique with high efficiency in terms of capacity and serviceability.

Experimental investigation and evaluation of shear performance of hollow slab beams strengthened by cavity grouting method

After 20 years of service, multiple web shear cracks were observed in 20 m-span prestressed concrete hollow slab beams. Shear enhancement is required to improve structural safety. To evaluate the strengthening effect of the new material on the hollow slab beam structure, fiber-reinforced cementitious composites (FRCC) were used to fill the cavities at the beam ends, and a comprehensive field load test was carried out on the shear-resistant performance of the actual bridge. The web principal stresses changed before and after strengthening under various working conditions, which were analyzed and compared with the performance of the traditional channel steel technique. The findings show that the web principal stresses are significantly reduced by more than 50 % after filling with FRCC, notably superior to the channel steel technique. In addition, both methods can reduce mid-span deflections by 10–20 %. The channel steel technique specifically enhances transverse connection capabilities. Furthermore, strain responses in the beam end sections were reduced by about 30–45 %. Finally, finite element simulations of single beam strengthening were also conducted to complement the experimental analysis. The simulation results show that the shear span ratio (λ), FRCC length and strand prestress loss remarkably impact the strengthening effect. The ultimate load capacity of the strengthened specimens decreases with the increase of λ and prestress loss and increases with the increase of FRCC length. In conclusion, the utilization of FRCC presents a superior alternative for shear enhancement in prestressed concrete hollow slab beams, offering substantial reductions in web principal stresses and enhanced structural performance compared to the traditional strengthening method.

Multi-physical analysis of saturation-dependent creep behavior for RC beam under sustained load and wet-dry cycles

A multi-physical and multi-scale analytical method based on thermo-hydro-mechanical models is adopted to evaluate the long-term deflection of RC beams with cracking under sustained loads and cyclic wet-dry conditions. The major physical-mechanical coupling mechanisms considered in this study includes: 1) water transport and phase equilibrium in the microstructure of gel and capillary pores; 2) accelerated moisture transport affected by cracking in concrete; 3) saturation-dependent creep coefficient considering gel and capillary pores; 4) combination of creep deformation and non-uniform shrinkage. The numerical approach is firstly verified by experiments where the thermo-hydro-mechanical interactions are found to be well analyzed. Then, parametric cases of cyclic wet-dry conditions are investigated to achieve deeper and wider conclusions. It has been found that under the cyclic wet-dry ambient conditions, there is an extreme drying state for concrete members depending on the drying humidity and its period. For the long-term mid-span deflection of beams, generally it will grow faster if the drying humidity is lower, which owes to the saturation-dependent creep coefficient, which has been called as Pickett effect. Meanwhile, beam's bottom-side cracking caused by sustained loads may also accelerate the moisture transport, which leads to an uneven drying state between upper and lower part of beams and viaducts, and eventually causes up-warping of them. For some cases, this up-warping can be significant enough to alter the macroscale structural creep deformation. At last, the difference between wet-dry cycle and dry-wet one has also been discussed. It can be proved that for the long-term deformation under wet-dry cycles, the moisture state will greatly affect the time-dependency from many aspects, for which the thermo-hydro-mechanical numerical approach is beneficial and needed in practice.

Flexural fatigue behavior of ultra-high performance concrete under low temperatures

Ultra-high performance concrete (UHPC) shows superior mechanical performance, which leads to increasing applications in infrastructure constructions that are subjected to different loading (i.e., flexure, tension, compression, etc.) and environmental conditions (ambient, freeze, etc.). Among them, the flexural performance of UHPC under low temperatures (i.e., sub-zero temperature) is still little understood especially under fatigue loading. To investigate the flexural fatigue properties of UHPC under low temperatures, eleven UHPC prisms are subjected to cyclic bending at different stress levels from 0.40 to 0.80 (the ratio between applied maximum fatigue stress and static flexural strength) and temperatures of 20 °C, -10 °C, and -20 °C. Results indicate that the fracture interfaces for specimens under static and fatigue loading exhibit distinct differences. No fiber buckling appears for the monotonically-loaded specimens, while for specimens under fatigue loading, fibers buckled and fractured. Low temperature improves the mechanical properties of UHPC under monotonic loading due to enhanced matrix strength. Conversely, low temperature adversely affects the flexural fatigue performance of UHPC due to the cold brittleness nature of matrix and steel fibers, leading to the accumulation of matrix deterioration and the fracture of steel fiber. When the temperature drops from 20 °C to -10 °C and -20 °C, there is a 15.0 % and 12.7 % decline in the flexural fatigue strength of UHPC, respectively. In addition, low temperature accelerates the degradation of UHPC, resulting in a larger and faster accumulation of fatigue deformation, including tensile strain, mid-span deflection, and fatigue deformation modulus.

Theoretical investigation of the structural performance of multi–span reinforced concrete beams strengthened with FRCM systems

Few studies have reported on the flexural behavior of multi–span reinforced concrete (RC) structures strengthened using externally–bonded (EB) systems such as fiber–reinforced polymer (FRP) and fiber–reinforced cementitious matrix (FRCM) systems. This paper introduces a theoretical model that can accurately predict the flexural behavior of such structures with a focus on their rotational capacity (curvature) and their moment redistribution response between critical sections. Unlike the available models, the proposed model accounts for the variation in the structure’s stiffness during loading including that of the strengthened section. The model can precisely determine the failure mode, the rotational capacity of the formed plastic hinges and estimate the moment redistribution ratio (MRR) between the critical sections at any applied load. The efficiency of the model was validated against the experimental results of eleven FRCM–strengthened two–span RC beams (including two control beams) previously tested by the authors. A good agreement between the experimental and the theoretical results was obtained with average experimental–to–theoretical ratios of 1.0 and 0.99 for the load carrying–capacity and MRR, respectively. To accurately determine the mid–span deflections of continuous EB–strengthened structures, a new reduction parameter was incorporated in the CSA–A23.3–19 (2019) formulations to account for the variation in stiffness of the strengthened section. The new formulations substantially enhanced the prediction of the deflection capacity of the strengthened structures with an average experimental–to–theoretical ratio of 1.02 versus 1.7 when CSA formulations were used.

Research on and Model Analysis of Flexural Mechanical Properties of Basic Magnesium Sulfate Cement Concrete Beams.

This study presents a comprehensive investigation into the mechanical properties of Basic Magnesium Sulfate Cement Concrete (BMSC) in comparison to Ordinary Portland Cement Concrete (OPC) within reinforced concrete components. The main objective is to evaluate BMSC's applicability for practical engineering purposes, with a focus on its with early high strength, improved toughness, and superior crack resistance compared to conventional concrete. Experimental procedures involved fabricating beam specimens using OPC concrete with a C40 strength grade, alongside BMSC beams with varying strength grades (C30, C40, and C50). These specimens underwent bending resistance tests to analyze crack patterns and mechanical characteristics. The findings reveal that BMSC beams demonstrate enhanced bending and tensile properties at equivalent strength grades compared to OPC beams. Particularly, cracking mainly occurred at the mid-span region of BMSC beams, characterized by narrower cracks, indicating superior crack resistance. However, it was noted that the toughness of BMSC beams decreases as the strength grade increases. The maximum mid-span deflection of the BMSC test beam was smaller than that of the OPC test beam, which was 3.8 mm and 2.6 mm, respectively. The maximum crack width of the OPC beam was 4.7 times that of the BMSC beam. To facilitate practical implementation, the study developed calculation models for estimating the crack bending distance and ultimate bending distance in BMSC beams, offering valuable tools for engineering design and optimization. Overall, this research provides significant insights into the mechanical behavior of BMSC, presenting potential advantages for structural engineering applications.

Typhoon- and temperature-induced responses of a cable-stayed bridge

Long-span bridges are subjected to wind and temperature actions. Wind action is generally the governing load of long-span bridges in design, while temperature action is also significant. Accurate separation of typhoon- and temperature-induced responses is thus necessary for in-depth investigation of their effects and comprehensive evaluation of structural performance. This paper separates the temperature- and typhoon-induced responses of the Qingzhou Bridge by using a unified global analysis approach. The field-monitored meteorological data and structural responses collected from the structural health monitoring system installed on the bridge are analyzed in detail, with emphasis on the comparison of those during typhoon Higos (Signal No. 9) and a typical sunny day after the typhoon. Results show that the quasi-static variation of displacement and stress responses are higher on a typical sunny day than those during the typhoon period, which is out of intuition. Through the unified analysis, the temperature-induced responses are calculated, and the typhoon-induced responses can be separated. The temperature- and typhoon-induced longitudinal displacement, mid-span deflection, and stress of the girder are compared. The temperature-induced response accounts for a large part of the total quasi-static recording either on a typical sunny day or during the typhoon period, whereas typhoon caused significant dynamic responses. The typhoon-induced quasi-static and dynamic responses are also in good agreement with the wind tunnel test results. This case study demonstrates the effectiveness of the unified global analysis in separating the temperature effect.

Experimental Investigation of TR-UHPC Composites and Flexural Behavior of TR-UHPC Composite Slab

In this investigation, the effects of different fabrics with 0.20% carbon fiber textile (CFT), 0.21% glass fiber textile (GFT), and 0.25% basalt fiber textile (BFT) on the properties of TR-UHPC were investigated by axial tensile tests. A bending test of the BFT-UHPC pavement slab was carried out. In terms of axial tensile performance, the fiber textiles ranked in the following sequence: CFT, BFT, and GFT. Additionally, the corresponding increases in the initial cracking strength and ultimate tensile strength were 18.0% and 21.9% for the CFT, 12.0% and 16.0% for the BFT, and only 9.1% and 8.0% for the GFT, respectively. Increasing the textile reinforcement ratio of the BFT from 0.25% to 0.50% improved the cracking stress and peak stress of the specimen by 12.0% and 15.9%, respectively. Moreover, the ultimate strain of the 0.50%-BFT reinforcing case was 1.4 times that of the 0.25%-BFT reinforcing case and 2.6 times that of the unreinforced specimen in terms of ductility. The results of the stacking test on the BFT reinforced UHPC pedestrian slab indicate that the mid-span deflection of the test slab under normal use load is 0.775 mm, which is only 19.8% of the deflection limit. Additionally, the test slab remained in the elastic stage without any cracking. The BFT effectively enhanced the toughness of the UHPC thin slab after cracking. It is expected to be applied as a novel structure to bridge pedestrian slabs, bridge decks, and other thin UHPC members, thereby improving the durability and mechanical properties of bridge structures.

Experimental study and numerical simulation of adhesively bonded timber-concrete composite panels: bending behavior, adhesive shear and peel stress distributions

This study investigated the structural response of timber-plain concrete panels bonded with epoxy and PUR adhesives under a four-point bending load, both experimentally and numerically. Tests evaluating epoxy- and PUR-bonded glulam-plain concrete panels measured ultimate load (Fult), effective bending stiffness (EIeff), and mid-span deflection (∆ult). Shear stress within the adhesives was monitored using fiber optic sensors. Numerical simulations estimated Fult and EIeff with errors of 5% and 14%, respectively. These discrepancies may stem from assuming defect-free wood (e.g., no knots), idealized boundary conditions, uniform adhesive thickness assumptions, and unmeasured mechanical and damage properties of wood and concrete (Detailed error source analysis is available in Section 4). Qualitative validation involved comparing sensor-recorded shear stress with simulation results. A parametric study evaluated the effects of adhesive thickness (0.5, 1, and 3 mm), concrete-wood depth ratio (50/85, 85/85, and 150/85 mm/mm), wood type (spruce (Picea), beech (Fagus), and Azobe (Lophira)), concrete strength class (C12/15 and C30/37), and span length (2, 4, and 8 m) on the bending behavior of the panel, and the shear and peel stress distribution within the adhesive bond line. Shear stress prevailed over peel stress in the adhesives, with peel stress approaching shear stress as span length increased (max. τa / max. σa ∼ 3.5–7). The ultimate load typically resulted in concrete compression damage and wood fiber damage, influenced by the concrete strength class and wood type. Higher depth ratios led to tension damage in concrete, while adhesive thickness had a minimal impact on stress distribution and failure modes.

Development and assessment of sustainable steel-concrete composite beams with novel demountable shear connections

The design of sustainable steel-concrete composite beams (SSCCBs) with demountable shear connections (DSCs) for deconstructability can improve the problem of construction and demolition waste during these construction activities, and it also strengthens the sustainability of a building by allowing for easy dismantling and the reuse or recycling of structural components at the service load and easy replacing the damaged members to achieve the resilience capacity after earthquake. In this study, the structural configuration and concept design of novel SSCCBs using DSCs were firstly introduced. The nonlinear finite element models (FEMs) using the Abaqus software were validated in terms of the load versus mid-span deflection curves and failure modes of the similar composite beams given by the experimental data. A parametric study was implemented to identify the influence of the following variables: geometric size, strength grade, inclination angle and shape of concrete plug, diameter and strength grade of connected bolt, steel grade and width and grade of slab concrete. It was found that geometric size, grade and smooth shape of concrete plug could optimize the performance level of occupancy while bolt diameter and grade enhanced the reuse behavior at service loads. Additionally, increasing the bolt diameter and steel grade led to an increase by 8–10% in the equivalent ultimate strength and to decrease the ductility of the whole beams obviously. Bolt diameter, steel grade and slab width have quite influences on the stiffness due to increase the interaction degree of these prefabricated components. Based on the theoretical and parametric analysis results, simple design method of ultimate moment capacity for this SSCCBs with DSCs is proposed to facilitate design practice.

Flexural behavior of novel marine concrete filled CFRP-aluminum alloy tube member

This study proposes a novel marine concrete filled CFRP-aluminum alloy tube (CFRP-CFAT) member for marine engineering. Six specimens including one marine concrete filled aluminum alloy tube (CFAT) and five CFRP-CFAT specimens were tested under uniaxial bending to investigate the flexural behavior of CFRP-CFAT. The effects of CFRP pasting positions, CFRP layers and shear span ratio were investigated. The failure patterns, mid span deflection curves, distribution of the deflection curves, strain, ultimate moment, ductility, flexural stiffness were analyzed. The experiment results illustrate that the failure pattern of CFAT specimen can be improved by CFRP. With the increase in mid-span deflection, the neutral axis shifts towards the compression zone. CFRP enhances the flexural capacity of CFAT specimens, the enhancement of inner CFRP was slightly better. The shear-span ratio does not have a significant impact on the flexural capacity. Compared to CFAT specimens, the use of CFRP leads to a decrease in ductility due to its brittle fracture. Calculation methods for CFRP-CFAT stiffness and bending moment capacity considering the influence of CFRP were proposed.

Enhancing Flexural Resistance in Pre-Damaged RC Beams with Near-Surface Mounted GFRP Bar and Bolt Anchoring System

The objective of this research was to explore the mechanical properties and failure mechanisms of reinforced concrete beams (RC beams) strengthened with near-surface mounted (NSM) glass fiber-reinforced polymer (GFRP) bars. This study focused on evaluating the effect of various factors on the load-deflection response and failure patterns of RC beams, including pre-existing damage, end anchorage, bar length, bar number, and the condition of concrete cover. The tested RC beams were divided into three groups. The first group included undamaged and damaged control beams. The second group involved the strengthening of beams after inducing damage, with variations in bar length, number, and cross-sectional area. This group also included beams strengthened by GFRP bars with and without anchors. In the third group, the effects of different cover materials, cover bonding techniques, and anchor bolts on the strengthening bars were examined. The results of the experiment indicated a notable decrease in both cracking and maximum load capacity for beams that were pre-damaged. The inclusion of anchor bolts appeared to have a noticeable effect, enhancing the load-carrying capacity and reducing mid-span deflection. Opting for two bars proved to be more effective than using three bars, leading to a higher maximum load and improved ductility. Moreover, prioritizing the bonding of the concrete cover at the end of the bars was found to be more important than bonding in the area of maximum moment.

Deterministic and stochastic finite element modeling of reinforced concrete beams without stirrups containing plastic wastes

PurposeThe use of waste polyethylene terephthalate (PET) plastics derived from shredded bottles in concrete is not formalized yet, especially in reinforced members such as beams and columns. The disposal of plastic wastes in concrete is a viable alternative to manage those wastes while minimizing the environmental impacts associated to recycling, carbon dioxide emissions and energy consumption.Design/methodology/approachThis paper evaluates the suitability of 2D deterministic and stochastic finite element (FE) modeling to predict the shear strength behavior of reinforced concrete (RC) beams without stirrups. Different concrete mixtures prepared with 1.5%–4.5% PET additions, by volume, are investigated.FindingsTest results showed that the deterministic and stochastic FE approaches are accurate to assess the maximum load of RC beams at failure and corresponding midspan deflection. However, the crack patterns observed experimentally during the different stages of loading can only be reproduced using the stochastic FE approach. This later method accounts for the concrete heterogeneity due to PET additions, allowing a statistical simulation of the effect of mechanical properties (i.e. compressive strength, tensile strength and Young’s modulus) on the output FE parameters.Originality/valueData presented in this paper can be of interest to civil and structural engineers, aiming to predict the failure mechanisms of RC beams containing plastic wastes, while minimizing the experimental time and resources needed to estimate the variability effect of concrete properties on the performance of such structures.

Mechanical Properties and Loading Simulation of Unidirectional Laminated Slabs Made from Recycled Concrete with Manufactured Sand

To align with the trend of the development of prefabricated buildings, this study aimed to produce unidirectional laminated slabs by using recycled concrete with manufactured sand (RCM). Additionally, performance evaluation and loading simulation analyses were conducted on these unidirectional laminated slabs. The experimental results indicate that the mechanical characteristics of RCM closely approximate those of recycled aggregate concrete (RAC), and they are all higher than the design value. Under ultimate loading conditions, the mid-span deflection of laminated slabs fabricated with RCM surpasses its RAC counterpart by 5.9%, indicating a pronounced proximity in flexural performance between RCM and RAC laminated slabs. Concurrently, ABAQUS finite element software was used to compare and simulate the performance of the unidirectional laminated slabs. The difference between the deflection generated by the actual applied ultimate load and the deflection generated by the simulated ultimate load is about 7.1%, and the simulation results are very close to the experimental results. Based on the experimental results, the practical application of RCM unidirectional laminated slabs has high value in the field of construction engineering.

Tensile strength based two-phase fatigue process prediction model of prestressed UHPC beams

A fatigue process prediction model of prestressed UHPC beams was established leveraging the tensile strength contribution of UHPC; based on the stress analysis of the UHPC beam, the fatigue process was divided into two phases: uncracked and cracked. The calculation results of the model were compared with the test results in other literatures, and the applicability of the model was verified. A railway prestressed UHPC box girder was taken as an example, and the effects of UHPC strength, prestress value, stress amplitude, reinforcement ratio, and span on the fatigue properties were investigated. The results verified the availability of the fatigue process prediction model of the prestressed UHPC beam; the error of UHPC strain and mid-span deflection development during the fatigue process is within 7%. The investigation of parameters showed that the prestress value, stress amplitude, and span have a great influence on fatigue life, while UHPC strength has a minor impact. At the early stage of the fatigue process, UHPC strength has a massive influence on the growth of strain, while other factors have almost no effect. At the later stage of the fatigue process, the prestress value, stress amplitude, and span have a significant impact on the growth of strain.

Effects of silica fume and zeolite on the durability of engineered cementitious composite containing limestone powder and blast furnace slag in a magnesium sulphate medium

ABSTRACT Engineered cementitious composite (ECC) is a highly ductile high-performance fibre-reinforced cementitious composite whose design, mixing ratios and other important parameters can be optimised using the theory of micromechanics. This study investigated the effects of different quantities of silica fume and zeolite on the mechanical properties and durability of ECC specimens containing lime stone powder and blast furnace slag when treated in the 5% magnesium sulphate solution at 28, 150, 180 and 210 days of age. The results obtained showed that the compression strengths in lab environment were enhanced up to 25% at the age of 150 days by increasing the silica fume content of the ECC, whereas the modulus of rupture (MOR) and mid-span deflection (MSD) were decreased in all the specimens tested. Meanwhile, a 17% increment in blast furnace slag content was observed to enhance both MSD and MOR at all ages, e.g. it causes 23% increase in MSD and 9% increase in MOR at the age of 28 days. In addition, a 46% increase in lime stone powder content was found to increase compressive strength but to reduce MOR by 7% and 8% at the age of 28 days, respectively.

Vibration Performance Evaluation of Cold-Formed Steel and Plywood Composite Floors

In this study, experimental natural frequencies and mid-span deflections were used to assess the tested composite floors against vibration serviceability limit states adopted by different standards such as AS3623. It was found that existing design criteria have predicted inconsistent results. Further, the finite element (FE) model was created, updated, and validated against the experimental modal parameters. The validated numerical model examined how various design parameters, such as material properties, cross-section geometry, and achieved a degree of composite action, have influenced the vibration properties such as natural frequencies and mode shapes. It was shown that as the added mass became more dominant than the stiffness enhancement, the fundamental natural frequency of the floor system dropped. This was evident from the results of the plywood slab thickness and the added permanent load parameters. On the other hand, the fundamental natural frequency increased with thicker and deeper joist sections since they made the floor system stiffer.

Performance of recycled aggregate concrete composite metal decks under elevated temperatures: a comprehensive review

ABSTRACT This comprehensive review explores the performance of composite metal decks and structural elements incorporating recycled aggregate concrete (RAC) at elevated temperatures. Despite the acknowledged environmental benefits of using recycled aggregates in concrete production, there is a notable gap in the literature regarding their behaviour under fire conditions. The investigation delves into studies encompassing fire resistance, physio-thermal properties, mechanical attributes, and structural performance of composite metal decks constructed with RAC. The analysis reveals that the inclusion of recycled aggregates has both positive and negative impacts on these elements when exposed to high temperatures. The fire resistance of metal decking composite slabs is significantly influenced by material properties, composition, and RAC mix design. Experimental findings indicate that RAC slabs showed larger midspan deflection under load and fire exposure compared to their counterpart NC slabs. After 120 min. of duration, the mid-span deflection of RAC-0 was recorded to be 19 % higher than the corresponding deflection of NC-0 slab. While temperature-time curves show comparable performance between RAC and natural concrete (NC) slabs, RAC slabs exhibit a notably lower ratio of soffit temperature to the upper surface temperature, resulting in increased spalling. In conclusion, this study advocates for the broader utilization of RAC in constructing structural elements, particularly composite slabs facing extreme temperatures. However, it emphasizes the need for additional research to optimize fire resistance and gain a comprehensive understanding of their behaviour. The findings provide essential guidance for structural engineers and researchers involved in the design of sustainable and fire-resistant structures.

Monitoring damage of concrete beams via self-sensing cement mortar coating with carbon nanotube-nano carbon black composite fillers

Self-sensing concrete used in coating form for structural health monitoring of concrete structures has the merits of cost-effectiveness, offering protective effect on structural components, enabling electrical measurements unaffected by steel reinforcement and is also convenient to maintain and replace. This paper investigates the feasibility of using self-sensing cement mortar coating containing carbon nanotube-nano carbon black (CNT-NCB) composite fillers (CNCFs) for damage monitoring of concrete beams. The self-sensing cement mortar coated to concrete beams demonstrated outstanding electrical conductivity (resistivity ranging from 18 to 85 Ω·cm). Under monotonic flexural loadings, self-sensing cement mortar coating with 1.8 vol.% CNCFs featured sensitive self-sensing performance in terms of capturing the initiation of vertical cracks at pure bending span of concrete beams, with fractional change in resistivity (FCR) reaching up to 60.6%. Moreover, FCR variations of self-sensing cement mortar coating exhibited good synchronization and stability with the variation of mid-span deflections of concrete beams during cyclic flexural loadings irrespective of the contents of CNCFs and cyclic amplitudes. Remarkably, it was found that FCR of cement mortar coating basically showed a progressive upward tendency, representing irreversible increase in the resistance during cyclic loading. The irreversible residual FCR indicated the crack occurrence and damage accumulation of concrete beams.

Fatigue Characteristics of Steel–Concrete Composite Beams

Fatigue in steel–concrete composite beams can result from cyclic loading, causing stress fluctuations that may lead to cumulative damage and eventual failure over an extended period. In this paper, the experimental findings from fatigue loading tests on composite beams with various arrangements are presented. Fatigue tests were performed up to 1,000,000 cycles using four-point loading, encompassing various ranges of shear stress at a consistent amplitude. Additionally, the effects of external post-tensioning and the strength of the shear connection were investigated. Static tests were run until failure to assess the enduring strength of the specimens subjected to fatigue. The cyclic mid-span deflections, slippages, and strains were measured during the testing. Based on the experimental findings, it was found that the damage region that the shear studs caused in the concrete slab, which resulted in a reduction in stiffness within the shear connection, grew as the loading cycles increased, leading to an increase in residual deflections and plastic slippages. Controlling the longitudinal fatigue cracks in the concrete slab was largely dependent on the strength of the shear connection between the steel beams and concrete slabs. Moreover, the applied fatigue loading range affected the propagation and distribution of fatigue cracks in the concrete slab. The strains in different parts of the composite specimens were significantly reduced by applying the external post-tensioning. With no signs of distress at the anchors, the tendons displayed excellent fatigue performance.