Brittle Shear Research Articles

Reinforcement Corrosion in RC Hollow Piers: Destructive and Non-Destructive Tests

In this work, cyclic-load tests on reduced-scale corroded reinforced-concrete hollow cross-section bridge piers have been experimentally performed and compared to the results of similar non-corroded piers. Piers were aged by using an imposed electric current and sodium chloride water solution before performing a mechanical cyclic-load test. The corrosion process has been detected with Non-Destructive Evaluation techniques by means of SonReb method (to check concrete degradation) and by measuring corrosion potential (to check steel degradation). The crack pattern was recorded by dedicated cameras, and an LVDT system was set up to monitor the cyclic-load test. Experimental results focused on degradation monitoring and mechanical performance under cyclic loads. During the cyclic-load mechanical test, the first cracks on the piers surface occurred diagonally, inclined at about 45°. This is the consequence of the failure mode change from ductile failure, as expected for slender designed piers, to brittle shear failure. The flexural failure occurred in the case of non-corroded piers. Presented tests can provide a useful contribution of experimental data to analyse the behaviour of corroded reinforced concrete hollow bridge piers, scarcely tested. In particular, the cyclic response can be a useful reference for the proposition/validation of nonlinear capacity models for the evaluation of the seismic capacity of corroded bridge piers.

Experimental and numerical investigations of the effects of various tensile reinforcement types on the structural behavior of concrete bridge deck slabs

Fiber-reinforced polymers (FRPs) have attracted attention owing to their ability to solve steel corrosion problems. However, FRP-reinforced concrete (RC) deck slabs were found to fail in a brittle shear manner due to the low stiffness of the FRP bars. In contrast, steel-RC deck slabs failed in ductile flexural failure by yielding of steel reinforcement. This study attempts to avoid such brittle failure in FRP-RC slabs by using hybrid steel/FRP bars that can provide serviceability, high strength, and durability. Seven full-scale reinforced concrete bridge deck slabs were cast and tested under four-point loading up to failure. The slabs were 3100mm length × 1000mm width × 200mm thickness. The investigated parameters were the reinforcement type and ratio and different patterns of the hybrid system. Subsequently, a finite element model was constructed, and the model results were compared to the experimental test results. Moreover, a numerical study was carried out by studying the different parameters affecting the shear behavior of RC members, such as the reinforcement ratio, FRP-to-steel ratio and wide range of the shear span-to-depth ratio. Based on the test results, Hybrid-RC slabs showed flexural-shear or compression-shear failure with ample warning than that reinforced with pure BFRP bars. Increasing the reinforcement ratio enhanced the overall slab performance at serviceability limit state. Furthermore, the numerical study indicated that the FRP-to-steel ratio should be Af/As ≤ 1.0 for achieving favorable ductile failure.

Modelling of CFRP-Strengthened RC Shear Walls with a Focus on End-Anchor Effects

This study first provides an overview of the development of a novel tube anchor system for the seismic strengthening or repair of reinforced concrete (RC) shear walls with carbon fibre-reinforced polymer (CFRP) sheets. The new anchor system can significantly improve the load transfer mechanism between the CFRP and supporting RC structural elements, resulting in ductile behaviour of the strengthened shear walls with increases of lateral load capacity and ductility by up to 2.6 and 8.3 times, respectively. The study then presents a new finite element modelling technique capable of capturing the complete cyclic response, i.e., from the elastic behaviour to the ultimate collapse of CFRP-strengthened RC shear walls with the newly developed tube anchor system. Two different modelling approaches are proposed to consider the effects of the tube anchor system. Additionally, other important CFRP- and RC-related mechanisms, including CFRP debonding effects, confinement enhancement, tension stiffening, compression softening, and strength and stiffness degradation under cyclic loads, are also considered in the model. By comparing the analytical and experimental results, it is demonstrated that the proposed modelling approach can accurately replicate the complex behaviour of CFRP-strengthened shear walls with a wide range of aspect ratios, from the ductile flexural behaviour of slender walls to the brittle shear failure of squat walls, without requiring detailed modelling of the anchor system.

Nonlinear finite element investigations on different configurations of exterior beam-column connections with different concrete strengths in column and floor

The fast development of quality concrete production has increased the usage of high-strength concrete (HSC) in the columns of high-rise buildings where high axial column loads exist. In contrast, normal-strength concrete (NSC) is used in the floor system for economic reasons. This produces a weak concrete zone at the intersection of columns and floors. Studies focused on evaluating the performance of such connections are still limited. The current numerical study investigates the performance of such connections. The developed numerical model has been verified against the experimental test for connections with different column-to-beam strengths. The numerical model has demonstrated acceptable accuracy compared to the experimental results. Moreover, the validated model has been employed to investigate the influence of different column-to-floor strengths on connections with and without transverse beams and floor slabs. It has been found that the strength and stiffness of connections with different concrete strengths have been improved compared to monolithic connections. Furthermore, the increase in joint strength and stiffness for connections with different column-to-floor strengths is more pronounced for connections with transverse beams and floor slabs due to their contribution to achieving proper confinement conditions for the weak concrete in the joint zone. In addition, the presence of a transverse beam affects the induced stress of the beam bars, resulting in a change in the mode of failure to beam flexural failure, whereas the presence of a slab floor increases both the stiffness and flexural strength of the beam. However, connections with the floor slab suffered high damage due to the transferred equilibrium torsion. Moreover, connections with different column-to-floor strengths exhibited larger stains in their joint stirrups; hence, additional joint stirrups are recommended to avoid the brittle shear failure of the joint. The study ended by evaluating the response of such connections under high axial column loads. It has been observed that planer connections perform poorly in terms of strength and ductility, while adequate performance has been observed for connections with transverse beams or slabs. Therefore, the role of the transverse beam and slab should be taken into account in the design of the connections with different column-to-floor strengths.

Influence of Peat Soil Environment on Mechanical Properties of Cement-Soil and Its Mechanism

The influence of peat soil environment (PSE) on the mechanical properties of cement-soil in the area around Dianchi Lake and Erhai Lake in Yunnan Province has attracted much attention. This study explores the change law of cement-soil UCS in the PSE, and provides guidance for the development and sustained usage of peat soil foundation. The paper discusses the preparation of cement-soil samples by adding humic acid (HA) and cement to cohesive soil with low organic matter content (blending method) and soaking it in fulvic acid (FA) solution and deionized water (steeping method) to simulate the actual working environment of cement-soil. Unconfined compressive strength (UCS), acid consumption, ion leaching, scanning electron microscope (SEM), and X-ray diffraction (XRD) tests are carried out on cement-soil samples soaked for 90 days. The results show that HA can significantly reduce the UCS of cement-soil. FA can reduce the UCS of cement-soil when the content of HA is less than 18%. However, when the amount of HA is more than 18%, the UCS of cement-soil increases slightly. FA makes the deformation and failure type of cement-soil gradually change from brittle shear failure to plastic shear failure. FA reacts with the cement hydration products in the sample so that the cumulative acid consumption of the cement-soil sample continues to increase, and the dissolution of Ca2+, Mg2+, Al3+, and Fe3+ in the sample increases the ion concentration of the soaking solution. In addition, SEM and XRD show that HA can increase the macropores and connectivity of cement-soil, while FA fills part of the pores of the wetting layer. In the PSE, FA can strengthen the inner structure of HA particles and fill and cement the layers of cohesive particles, enhancing the construction of cement-soil with HA content greater than 18%, so that its UCS is relatively improved. However, when the amount of HA is less than 18%, there are more small pores in the cement-soil. The interaction between FA and HA in the cement-soil is weak. The influence of FA on cement-soil is mainly a weakening effect, and its UCS is relatively reduced.

A Brief Overview on Crack Patterns, Repair and Strengthening of Historical Masonry Structures.

Given that a significant fraction of buildings and architectural heritage in Europe's historical centers are masonry structures, the selection of proper diagnosis, technological surveys, non-destructive testing, and interpretations of crack and decay patterns is paramount for a risk assessment of possible damage. Identifying the possible crack patterns, discontinuities, and associated brittle failure mechanisms within unreinforced masonry under seismic and gravity actions allows for reliable retrofitting interventions. Traditional and modern materials and strengthening techniques create a wide range of compatible, removable, and sustainable conservation strategies. Steel/timber tie-rods are mainly used to support the horizontal thrust of arches, vaults, and roofs and are particularly suitable for better connecting structural elements, e.g., masonry walls and floors. Composite reinforcing systems using carbon, glass fibers, and thin mortar layers can improve tensile resistance, ultimate strength, and displacement capacity to avoid brittle shear failures. This study overviews masonry structural diagnostics and compares traditional and advanced strengthening techniques of masonry walls, arches, vaults, and columns. Several research results in automatic surface crack detection for unreinforced masonry (URM) walls are presented considering crack detection based on machine learning and deep learning algorithms. In addition, the kinematic and static principles of Limit Analysis within the rigid no-tension model framework are presented. The manuscript sets a practical perspective, providing an inclusive list of papers describing the essential latest research in this field; thus, this paper is useful for researchers and practitioners in masonry structures.

Post-Earthquake Fire Punching Shear Behavior of GFRP-Reinforced Slab-Column Connections

It is not uncommon for reinforced concrete slab-column assembly to experience a punching brittle shear failure type under seismic loading. This research work numerically investigates the punching shear behavior of interior GFRP-reinforcedslab-column connections under post-earthquake fire. Two experimental results reported in the article were used for validation analysis using ANSYS nonlinear finite element software program. Further, parametric studies on influential variables such as fire exposure duration, concrete grade, slab thickness, fire exposed surface, and column aspect ratio were performed to get insight into the post-earthquake fire behavior of GFRP-reinforcedslab-column connections. Finite element analysis results showed decreasing fire exposure duration, enhancing grades of concrete, increasing slab thickness, minimizing fire exposure surfaces, and increasing column aspect ratio, which improved the punching shear capacity of GFRP-reinforced slab columns. Moreover, increasing slab thickness provided good performance against post-earthquake fire loading as compared to enhancing concrete grades in GFRP-reinforcedslab-column assemblies. The research concludes that it is crucial to take post-earthquake fire into account when designing structures to ensure no collapse safety design requirements.

Punching shear code provisions examination against the creation of an opening in existed RC flat slab of various sizes and locations

Punching shear is a critical problem in flat slabs directly supported at columns resulting in a high-stress concentration area, increasing the probability of brittle punching shear failure. However, the capacity is reduced by creating an opening that affects the overall behavior of the slab based on its size and location with respect to the loaded area. Furthermore, the design and analysis of the various structural elements are based on international regulations that have major differences in their basis and executions. In this study, the different code provisions in punching shear of RC two-way flat slab without shear reinforcement are examined under various opening sizes and locations using the Nonlinear Finite Element Analysis (NLFEA) procedure using ABAQUS software. A total of twenty-one model has been simulated for examining the prediction accuracy by the ACI318-19, MC2010, and EC2 under the effect of opening size (100, 200, and 300) mm, and locations (zero, 0.25d, 0.50d, 2.0d, 4.0 h, 5.5d, and 6.0d) under two main categories; the critical punching perimeter, and the critical opening location. However, it has been revealed that the proposed value of 0.50d as the critical punching perimeter is the most reliable one; besides, the value of 4 h is enough for defining the position where the effect of an opening could be neglected regardless of its size. Furthermore, it has been found that the column-to-opening ratio (C/O) is a very significant factor in controlling the punching shear capacity prediction accuracy by the different codes. Predictions get more overestimated under larger (C/O) values where increasing the C/O ratio by half increases the ultimate deflection percentage by an average of 22 %, except for those with smaller C/O values of less than 0.5, where it only reaches a maximum value of 13 %. Moreover, code prediction of the ACI318-19 and the MC2010 was found to be overestimated in all cases. In contrast, the EC2 was underestimated with an accurate prediction for an opening location of 2.0d from the column's face. However, it has been found that ACI318-19 is the most accurate one regarding the critical punching perimeter (0.5d) and critical opening location (4.0d).

Bond-slip Behaviour of NSM GFRP Bars in Reinforced Recycled-Aggregate Concrete: Experiments and a Modified Model

Bond-slip behaviour of glass fiber-reinforced polymer (GFRP) bars embedded in conventional concrete has been widely investigated. In contrast, the bond-slip behaviour of near-surface mounted (NSM) GFRP bars bonded in reinforced recycled aggregate concrete (RAC) seems to be less explored, while recycled materials have been increasingly used due to reasons of environmental pollution and resource exhaustion. This study aimed to experimentally and theoretically examine the bond-slip behaviour of NSM GFRP bars in reinforced RAC under monotonic and cyclic loadings. To achieve this aim, twenty-four tests were performed, which were divided into two groups by monotonic and cyclic loadings. In each group, twelve tests were performed on ten reinforced RAC specimens and two reinforced normal aggregate concrete (NAC) specimens. The test results confirmed the brittle shear failure of concrete in the proximity of a resin-concrete surface. Bond-slip behaviour can be characterized by nonlinear and linear branches, in which the linear branch dominates the behaviour. Under monotonic and cyclic loadings, the average slips of GFRP bars in reinforced RAC were 0.238 and 0.284 mm, and their coefficients of variation (COV) were relatively large at 0.142 and 0.130, respectively. In contrast, ultimate loads had a relatively low COV of around 0.038. The effect of cyclic loading significantly increased the ultimate slip by 19.3%, whereas it negligibly reduced the ultimate load; consequently, the stiffness was reduced by 19.4%. A modified smooth model was proposed to predict the bond-slip behaviour of NSM GFRP bars in reinforced RAC under monotonic and cyclic loadings. The simplicity and accuracy of the model can be useful for engineers in structural retrofitting using NSM FRP technique. Doi: 10.28991/CEJ-2023-09-02-01 Full Text: PDF

On the Scale‐Dependence of Fault Surface Roughness

AbstractDefining roughness as the ratio of height to length, the standard approach to characterize amplitudes of single fault, joint and fracture surfaces is to measure average height as a function of profile length. Empirically, this roughness depends strongly on scale. The ratio is approximately 0.01 at a few mm but 10× smaller at a few tens of meters. Surfaces are rougher at small scales. However, these conclusions are metric‐dependent. If instead height is averaged over wavelength, roughness is nearly Brown spatial noise, having almost scale‐independent apparent surface height to wavelength ratio. The small deviation from scale‐independence is of the opposite sense than found using the standard metric; surfaces are slightly rougher at long wavelengths. Some natural surfaces may be Brownian within the measurement uncertainties. These contradictions are curiosities of surfaces that have Hurst exponents between 0.5 and 1, as natural fault surfaces do. The wavelength‐based analysis of roughness and how it changes with scale are straight‐forward; a normalized Fourier transform approximately preserves amplitude and its scale dependence in the wavelength domain. Among the conclusions from reconsideration of scale dependence are that the scale dependence is weak and much smaller than that of other fault and shear zone properties. Background and aftershock seismicity, jogs and step‐overs indicate strong localization (smoothing) with slip and scale. The lack of strong scale dependence to surface roughness suggests it is not the dominant control on brittle shear zone evolution.

Evaluation of seismic performance of precast concrete walls with X-shaped steel plate bracings

Structures utilizing precast concrete walls have wide usage around the world, yet previous earthquakes have revealed the seismic performance of those walls is often deficient. These deficiencies can result in shear sliding at the wall base or brittle shear failure of the wall. These failure modes have been shown to be suppressed through the use of diagonal reinforcement in cast-in-situ walls, however, the tolerances and reinforcement geometry make the use of diagonal reinforcement in precast walls very difficult to achieve. In this paper, as an alternative to traditional diagonal reinforcement, X-shaped steel plate bracing was adopted in precast concrete walls and connected with welded joints. The experimental tests of four walls are presented, all of which incorporated the bracing and used either a cast-in-situ or bolted steel connection. The influence of the foundation connection and X-shaped steel plate bracing on the seismic performance of walls with different shear span ratios is described. The X-shaped steel plate bracing was found to effectively control shear sliding, with a greater decrease in shear sliding for walls with a lower shear span ratio. The bracing improved the peak strength of the walls, but the improvement varied with the angle of the bracing. The precast concrete walls with X-shaped steel plate bracing performed similar flexural failure modes to the reinforced concrete walls with a low shear span ratio but formed a plastic zone at the mid-height of the wall panel for the precast wall with a shear span ratio of 2.282. Numerical models developed for the precast concrete walls were able to estimate the force-displacement relationships.

A Design Process for Preventing Brittle Failure in Strengthening RC Slabs with Hybrid FRP-HPC Retrofit Systems.

The retrofitting of existing RC slabs with an innovative system comprising FRP and HPC has been demonstrated to be effective in strengthening and overcoming the logistical challenges of installation. Nonetheless, the excessive improvement of flexural strength over shear strength would cause the sudden failure of rehabilitated flexural members. The literature has previously recommended failure limits to determine the additional moment strength compared with the shear strength to prevent brittle shear failure of strengthened, continuous RC slabs. This study suggests a design process for preventing shear failure and inducing the ductile-failure mode to improve the safety and applicability of retrofitted RC slabs based on the proposed failure limits. The effectiveness of the procedure in brittle-failure prevention for the end and interior spans of retrofitted RC slabs is illustrated via a case study. The outcomes showed that the retrofit system with 0.53-mm-thick-CFRP prevented brittle failure and significantly enhanced the design-factored load and ultimate failure load by up to 2.07 times and 2.13 times, respectively.

Geology of the Copper Mineralization in Proterozoic Ajabgarh Meta-Sediments of, Dokan-Dariba Belt, Sikar District Rajasthan Northwestern India

The Khetri copper belt is a well-known metallotect in northern part of Delhi fold belt in Rajasthan. On the eastern margin of the Khetri sub basin of North Delhi basin separated by a basement high, another sub basin Alwar-Ajabgarh sub basin exposes that a thick sequence of Ajabgarh group of rocks overlies a thick arenaceous sequence of Alwar group of Delhi Super Group of rocks. The Ajabgarh meta sediments here in the Neem Ka thana area are characterized by presence of Bornite dominated copper mineralization with silver association and minor presence of Pb. The mineralization has been described by various workers as strata-bound, hypogene and IOCG. But these inferences are based on part information and the inference drawn is sectorial in nature. The current study includes a holistic study based on exploration over a period of more than two decades and the data generated suggest thereof, that this syngenetic sulphide mineralization associated with the sedimentation of marl and carbonate rocks. Subsequently it has been relocated during 2nd deformation accompanied by epigenetic component of mineralization depicted in terms of vein filled coarse grained aggregates of bornite and chalcopyrite disposed across the general disposition of litho-package. The EPMA and fluid inclusion data generated from the area indicate association of typical hydrothermal environment minerals like, Perkrite, Wittchenite, Aguilarite, Molybdnite etc. The mineralizing fluids have been trapped between the temperature ranges of 130°C to 375°C with average being 250°C to 300°C. The fluid salinity also varies from near pure hot water to moderately saline fluid indicative of multi-episodic mineralization of syngenetic nature coupled with epigenetic component. The ore textures indicate 500°C temperature range; certain intergrowths of minerals like specular hematite and bornite suggest the occurrence of hypogene environment induced due to emplacement of granite/pegmatite on the eastern and southern margins of the belt. The strata bound nature suggests the euxogenic environment facilitated by carbonate facies of rocks. The parallelism of sulphide with the rock fabric was attained during first deformation and the epigenetic component coupled with the hypogene assemblage was deposited during the D2 deformation in the brittle ductile shear zones and limb shears, between the temperature ranges of 130°C to 570°C as deduced from petrochemical data. Hence a comprehensive model is suggested here on evolution of process of mineralization in the Neem Ka Thana belt.

An Experimental and Numerical Evaluation of the Structural Performance of Concrete Beams Containing Bamboo Shear Reinforcement

Alternatives to steel reinforcement in concrete are being actively investigated for environmental, economic, and durability concerns. Several studies suggest that bamboo is a potential substitute for steel reinforcement. In this study, the shear behavior of five reinforced concrete beams incorporating bamboo strips as shear reinforcement at different spaces and configurations were assessed. Structural concrete having a compressive strength of 25 MPa was used for this purpose. The experimental program involved applying four point bending test to the beams to determine their load deflection curves, crack pattern, and strain distribution. In addition, a numerical analysis was conducted for validation and prediction purposes. It was observed that including bamboo strips as shear reinforcement influenced a more brittle behavior with marginal differences when changing their spacing. On the contrary, the spacing was decisive for the load carrying capacity, as smaller spacing caused higher capacity. Strain distribution results followed a similar pattern to that of the deflection. All the curves exhibited a brittle shear failure evidenced by the crack propagation process. Further, the numerical study performed produced accurate results in comparison with the results obtained experimentally, in terms of both the load deflection curves and the crack pattern.

An Experimental and Numerical Evaluation of the Structural Performance of Concrete Beams Containing Bamboo Shear Reinforcement

Alternatives to steel reinforcement in concrete are being actively investigated for environmental, economic, and durability concerns. Several studies suggest that bamboo is a potential substitute for steel reinforcement. In this study, the shear behavior of five reinforced concrete beams incorporating bamboo strips as shear reinforcement at different spaces and configurations were assessed. Structural concrete having a compressive strength of 25 MPa was used for this purpose. The experimental program involved applying four point bending test to the beams to determine their load deflection curves, crack pattern, and strain distribution. In addition, a numerical analysis was conducted for validation and prediction purposes. It was observed that including bamboo strips as shear reinforcement influenced a more brittle behavior with marginal differences when changing their spacing. On the contrary, the spacing was decisive for the load carrying capacity, as smaller spacing caused higher capacity. Strain distribution results followed a similar pattern to that of the deflection. All the curves exhibited a brittle shear failure evidenced by the crack propagation process. Further, the numerical study performed produced accurate results in comparison with the results obtained experimentally, in terms of both the load deflection curves and the crack pattern.

Shear behavior of concrete beams reinforced with corrosion-resistant and ductile longitudinal steel-FRP composite bars and FRP stirrups

Inheriting excellent corrosion resistance of FRP bars, steel-FRP composite bar (SFCB) has better elastic modulus and ductility, promising to be longitudinal reinforcement for concrete structures in harsh environments. While previous research primarily focused on the flexural behavior of hybrid longitudinal SFCB and FRP stirrups reinforced concrete (hybrid-RC) beams, the study about shear behavior has rarely been reported and valuable experimental observations are limited. The unique mechanical properties of SFCB causes the inapplicability of existing shear design method and the risk of brittle shear failure. Here, a simplified shear design method is proposed for hybrid-RC beams by analytical investigation and the shear behavior of hybrid-RC beams is investigated experimentally. Results show that SFCB exhibits similar transverse shear behavior to steel bar. Compared with steel bars reinforced concrete beams, hybrid-RC beams based on the proposed design method have better shear performance including same failure modes, similar deflection, narrower shear crack, and higher shear capacity, due to the post-yielding stiffness of SFCB. Furthermore, a modified calculation method of the shear capacity for hybrid-RC beams is proposed, exhibiting great feasibility and accuracy. These results can provide valuable experimental observations of shear behavior and promote the development of shear design tactics for hybrid-RC beams.

Strengthening method by using ultra-high-strength fiber-reinforced concrete panels for a column on the soft first story of a reinforced concrete building

This paper presents a simple and efficient strengthening method by using ultra-high-strength fiber-reinforced concrete (UFC) panels on the soft first storys of reinforced concrete (RC) buildings at the risk of story collapse or shear failure of column due to earthquakes. Five 1/3 scale specimens, which replicated RC columns on the soft first story of a 10-story condominium building heavily damaged by the 2016 Kumamoto Earthquake, were constructed and tested. One of these was a reference specimen (no strengthening), and the other four were strengthened by attaching UFC panels on the two faces parallel to the assumed loading direction with or without an UFC or a RC wing wall on either column side. Cyclic lateral and varying axial loads were applied to the specimens to emulate earthquake loads. Load–deformation hysteretic responses, failure modes, and the responses of the UFC panels and the wing walls, are discussed in detail. The experimental results revealed that the reference specimen (without strengthening) had a low-load-carrying capacity and exhibited brittle shear failure, as observed in the actual building during the earthquake. Conversely, the strength and deformation capacities of the strengthened specimens improved considerably, and the effectiveness of the proposed strengthening method was validated quantitatively.

Numerical study on shear capacity of geometrically similar RC interior beam‐column joints

Reinforced concrete (RC) beam-column joints often present brittle shear failure in the core area. The objective of the study is to study the effects of stirrup ratio and axial load ratio on the shear capacity of geometrically similar beam-column joints having different structural sizes. In this work, a series of 3D mesoscale simulations on the shear failure of RC beam-column joints were conducted and validated, in which the concrete heterogeneity was considered explicitly. The simulation results indicate that stirrups can improve the shear strength of joints, enhance the ductility, improve deformation ability, while weaken the size effect on the nominal shear strength. Moreover, the increasing axial load ratio would lead to the increase of shear strength, as well as the increase of size effect. Based on the modeling results, a novel semiempirical and semitheoretical size effect law considering the quantitative effect of stirrups and axial load ratio was proposed. In addition, the proposed size effect law was verified against with some available test data.

Experimental investigation and simulation on load-transfer paths in optimally designed RC deep beams

The main failure pattern for reinforced concrete deep beams is shear failure due to the low shear-span ratio. The Topology Optimization for the stress of rebar in this study is explored for aided-design of deep beams, which proves that the optimization can transform the brittle shear failure to ductile bending failure without reducing the bearing capacity of deep beams, compared with the traditional empirical method. In the process of increasing load, the displacement fields on the surface of the deep beams were measured successively by non-contact displacement gauges, and converted to the principal strain distribution. Then the distribution is used to fit correspondingly the principal stress trajectory and load-transfer paths of the specimens. The results show that, for the specimen designed with Topology Optimization, the built-in inclined main reinforcements are in line with the direction of the concrete tensile stress in the web of the specimens, and effectively restrict the development of width of the inclined cracks. Consequently, the integrity and directness of the load-transfer paths from the loading point to the supports are guaranteed. Meanwhile, the stress fields of the specimens correspond to the Michell-type structure, hence the stress of their rebar is almost under a full stress state. Therefore, the optimal design presents a more reasonable reinforcement layout, which can better control the accumulation of damage and the change of the load-transfer paths during the loading process, and finally achieve the desired failure pattern.

Experimental Study on the Bending and Shear Behaviors of Chinese Paulownia Wood at Elevated Temperatures.

Chinese Paulownia wood has been extensively used in the construction of timber buildings and lightweight sandwich structures. However, the bending and shear behaviors at elevated temperatures were not well understood. A total of 162 specimens were tested to investigate the bending, tangential shear, and radial shear performances of Chinese Paulownia wood under temperatures from 20 to 220 °C. It was found that the bending specimens exhibited ductile failure due to the progressive damage after reaching the peak load, while the tangential and radial shear specimens exhibited brittle shear failure along the shear plane. The elevated temperatures had limited effects on the failure modes. Under the same temperature, the retention rate of the modulus of elasticity is significantly higher than that of the modulus of rupture. Moreover, the bending strength, tangential shear strength, and radial shear strength generally and nonlinearly decreased with the increasing temperature. The EN 1995-1-2 design curve for the shear strength of wood at elevated temperatures is conservative for both the tangential and radial shear specimens. However, the design curve may not be adopted to estimate the tangential shear strength at temperatures higher than 220 °C.