Reduction In Shear Resistance Research Articles

Efficient beam-based model for reinforced concrete walls considering shear-flexure interaction

This paper presents an efficient beam-based modelling scheme for the seismic analysis of reinforced concrete structural walls. The model combines a force-based beam element with a fibre section for flexural response and a zero-length element for shear response. The fibre-based element simulates the nonlinear flexural behaviour through uniaxial material laws that account for concrete cracking, concrete crushing, and yielding and rupture of reinforcing bars. The zero-length element represents the shear behaviour with a trilinear lateral force-displacement curve representing, in a phenomenological way, nonlinear deformations caused by diagonal cracking. The reduction of shear resistance caused by inelastic flexural deformations is accounted for in the model to reproduce failures due to shear-flexure interaction. The model has been validated using data from 52 tests on wall specimens exhibiting flexure, shear and mixed shear-flexure modes from experimental campaigns reported in the literature, showing good accuracy in predicting the effective stiffness, maximum strength and displacement capacities obtained in the tests. Model results for ultimate displacement capacity correlate better with experimental results than simplified code-oriented expressions in performance-based evaluation standards and recommendations. Considering its balanced accuracy and computational efficiency, it is concluded that the proposed modelling scheme can effectively be used for performance-based seismic design and assessment of RC wall buildings.

Anchors to solid clay brick masonry in shear: Behavior under monotonic and cyclic loading

To investigate the behavior of injected anchors installed in solid clay brick masonry, an extensive experimental campaign was performed at the National Technical University of Athens (NTUA). The focus of the research is on the behavior in seismic conditions, to contribute to the design of relevant retrofitting applications. In this paper, the results of shear tests on metal injection anchors under monotonic or cyclic loading are presented. The anchors are installed in uncracked or cracked solid clay brick wallettes subjected to compressive stress of 0.2 MPa. The tests are performed under displacement-controlled conditions. In this part of the experimental campaign the main parameters investigated are the anchor location (in mortar joints or center of bricks), the presence of a crack crossing the anchor, the substrate properties (wallettes made with two different solid bricks, laid either in strong or in weak mortar) and the loading history (monotonic or cyclic). The experimental results illustrating the effect of the investigated parameters are presented, while the effect of cracking due to seismic loading and the reduction of shear resistance due to cycling are evaluated.

Effects of anobiid damage on shear strength parallel to the grain in single step joints

Traditional carpentry joints can be found worldwide in many timber truss structures connecting rafter and tie beam. One failure mode of this connection result from shear in the tie beam beyond the notch either due to bad design or deterioration. In this article, the reduction in shear strength of Single Step Joints (SSJ) resulting from biological attack by anobiids was analysed. For this purpose, tests were carried out in non-degraded scots pine (Pinus sylvestris L.) specimens (reference) and compared to artificially degraded specimens with three different levels of degradation. The reduction of shear resistance was analysed in relation to the density of holes drilled during the degradation simulation, the loss of mass, and the reduction of the shear-resistant area. At lower degradation levels, no significant reduction in shear strength was observed. On the other hand, the linear regression shows a trend of resistance reduction with increasing degradation. Despite the relatively low coefficient of determination (r2 = 0.25), the parameter that best correlated with the residual strength was the reduction in the shear-resistant area.

The assessment of structural behaviours of steel framing system – affordable house system design

Purpose Nowadays, residential buildings have become increasingly important due to the growing communities. The purpose of this study is to investigate the behavior of a steel structural framing system that incorporates lightweight load-bearing walls and slabs, and to compare the weight of materials used in cold-formed and hot-finished steel structural systems for affordable housing. Design/methodology/approach Four types of models consisting of 243 members were simulated. Model 1 is a cold-formed steel structural framing system, while Model 2 is a hot-finished steel structural framing system. Both Models 1 and 2 use lightweight wall panels and lightweight composite slabs. Models 3 and 4 are made with brick walls and precast reinforced concrete systems, respectively. These structures use different wall and slab materials, namely, brick walls and precast reinforced concrete. The analysis includes bending behavior, buckling resistance, shear resistance and torsional rotation analysis. Findings This study found that using thinner steel sections can increase the deflection value. Meanwhile, increasing member length and the ratio of slenderness will decrease buckling resistance. As the applied load increases, buckling deformation also increases. Furthermore, decreasing shear area causes a reduction in shear resistance. Thicker sections and the use of lightweight materials can decrease the torsional rotation value. Originality/value The weight comparison of the steel structures shows that Model 1, which is a cold-formed steel structure with lightweight wall panels and lightweight composite slabs, is the most suitable model due to its lightweight and affordability for housing. This model can also be used as a reference for the optimal design of modular structural framing using cold-formed steel materials in the field of civil engineering and as a promotional tool.

Shear resistance reduction of granular materials subjected to high-frequency and low-intensity vibration: A micro-mechanical study

高速铁路速度的进一步提升，需要解决轨下土工基础在高频振动作用下的稳定性问题。前期通过试验研究发现，即使在动应力水平相对较低的条件下，高频振动作用仍会导致颗粒材料出现流态化、强度衰减等一系列区别于低频振动的现象。这些现象的力学机理目前尚未完全明确，不利于未来更高速铁路的轨下土工基础设计。结合离散元数值模拟开展了双轴试验，分析了高频低幅振动下力链数量、各向异性及遗传颗粒等细观指标的演化规律，量化了颗粒材料中承载主体骨架结构的发展变化。结果表明，颗粒材料宏观偏应力的发展、波动等与细观力链的演化规律表现出较强的一致性；高频低幅振动作用下骨架结构的变异程度与抗剪强度衰减存在线性关系，骨架结构变异越大，归一化的抗剪强度衰减越大。

Thermodynamic basis of granular STZ model and its application in revealing shear resistance reduction mechanisms of granular soils under vibration

Thermodynamic basis of granular STZ model and its application in revealing shear resistance reduction mechanisms of granular soils under vibration

Performance of stud shear connections under combined shear and pull-out forces

This paper examines the structural behaviour of stud shear connections in solid concrete slabs under combined shear and pull-out forces. Nonlinear numerical simulations and parametric assessments are carried out using advanced finite element models which are validated and calibrated against detailed experimental results. Through realistic representation of yielding and ductile damage of the steel stud, as well as cracking and crushing of the surrounding concrete, the local ‘stress and strain’ conditions are evaluated and the underlying load transfer mechanisms within such connections are identified. It is found that the predicted resistance of the stud connections under shear forces in solid concrete slabs of various concrete grades compare favourably with codified design values. Importantly, however, it is shown that the corresponding shear resistance of these connections under various combinations of shear and pull-out forces exhibits a nonlinear reduction with the increase in the pull-out forces. The reduction in shear resistance of these connections reaches typically 15% to 20% for various concrete grades when a pull-out force of about 0.27 of the applied shear force is present. Based on the numerical results of the calibrated models, the effects of pull-out forces on the shear resistance of these connections are established and quantified. An interaction relationship for practical combinations of shear and pull-out forces for connections with various concrete grades is also proposed for design.

Effects of core air gaps and steel inserts on thermomechanical response of GFRP-balsa sandwich panels subjected to fire

Composite sandwich panels composed of a balsa core and glass fiber-reinforced polymer (GFRP) face sheets may offer attractive applications for building slabs and bridge decks. Such composite panels may contain air-filled gaps (caused by initial defects or damage) or through-thickness cracks and different types of metallic inserts (used for facilities and piping systems) in the balsa core. The fire performance of sandwich panels can be reduced by the local heating effects inside such air gaps and inserts. The thermomechanical response of GFRP-balsa sandwich panels comprising through-thickness air gaps or steel inserts, subjected to combined mechanical load and one-sided ISO 834 fire, were thus investigated by fire experiments and uncoupled thermal and mechanical numerical analysis. The results demonstrated that the shear resistance reduction of the core is not critical, while the moment resistance reduction can lead to panel failure. The propagation of a transverse tensile crack in the balsa core produced a similar moment resistance reduction to an air gap or steel insert. The air gaps and steel inserts charred the inner core zones and heated the cold face sheet above, leading to face wrinkling. The effects of air gaps and steel inserts remained local. Depending on their location in a panel, they may thus not exhibit significant effects on the whole structure. If they are placed on critical load paths however, e.g. in the vicinity of supports, they may cause collapse of the whole structure. Since the extension of transverse tensile cracks is not limited, they may also lead to an overall collapse.

Development of extended STZ model for granular soils subjected to combined static loading and vibration

The ‘shear-transformation zone’ (STZ), which may be referred to as a weak domain in granular material, is the main source of plastic deformations in non-cohesive soils such as sand or gravel. To theoretically investigate the vibration-induced shear resistance reduction (ViSRR) of granular materials, in this paper an extended STZ model is proposed that considers the coupling effect between vibration and quasi-static loadings. The framework of the model consists of three components: (a) the motion of STZs including the transition, creation and destruction of STZs; (b) the relation between the motion of small-scale STZs and the observable, macroscopic plastic strain; and (c) the evolution law of a ‘configurational temperature’ that reflects the energy that drives the motion of STZs. The conventional STZ model developed for amorphous materials is enhanced to accommodate both volumetric and shear deformations in the spatial stress state. Specifically, in addition to considering plastic shear strains induced by the change in STZ orientation as the result of the transition, as in conventional STZ models, the extended STZ model correlates plastic volumetric strains with the change in STZ amount resulted from creation and destruction.

Machine Learning-Aided Prediction of Post-Fire Shear Resistance Reduction of Q690 HSS Plate Girders

Fire has significant effects on the residual resistance of steel structures. It is necessary to accurately clarify its effects on Q690 HSS plate girders, which have been widely used. In this paper, the ultimate resistance and effective service resistance of Q690 HSS plate girders after a fire are obtained using material tests and finite element (FE) analysis including parametric studies, where the data of 210 models were collected. The effects of four key parameters (hw/tw ratio, a/hw ratio, exposure temperature and cooling method) on post-fire shear resistance reduction of Q690 HSS plate girders are roughly investigated by individual conditional expectation (ICE), showing exposure temperature is the most important factor. The popular algorithms of machine learning (ML), namely artificial neural network (ANN) and support vector regression (SVR) algorithms, are utilized in model training to predict the reduction factors of both ultimate resistance and effective service resistance. Finally, the results indicate that the prediction using ML shows much better performance than that with traditional ordinary least squares (OLS) regression, and SVR with genetic algorithm (GA) provides the highest prediction accuracy. The results of this paper show the superiority of machine learning for solving prediction problems of steel structures, compared with conventional methods such as linear regression.

The orientation effect of opening and internal strengthening on shear performance of deep concrete beam using recycled tyre steel fibres

A deep concrete beam is a structural member that transfers heavy loads from the introduced column(s) due to a change of function layout of a particular floor in the building. Due to its high depth, the service utilities are always accommodated by creating a transverse opening rather than at its soffit. However, this practice leads to a reduction of shear resistance and affects the serviceability of the beams. To reinstall this capacity, waste tyre steel fibres were used to assess their effectiveness in improving the shear resistance of the deep concrete beams with openings. Three sets of beams with, without fibres, and with fibre mesh that had openings of 160 × 86, 115 × 120, 86 × 160, and 165 × 170 mm were considered. A total of 16 beams with dimensions 150 × 400 × 1100 mm and a constant shear span-to-depth ratio of 0.8 were cast and tested. The steel fibres used had a diameter of 1.3 mm, a length of 50 mm, a fibre content of 0.5% and a fibre mesh of 110 × 100 mm. The main variables evaluated were the effect of the opening size and its orientation, the effect of stirrups, the random mixing of fibres in the matrix, and the internal strengthening of the fibre mesh in the anticipated strut line of the deep beam. The results showed that an interruption of the strut width affected the shear resistance of the beam. The beam with 160 × 86 mm had a lower capacity of 7.7% compared to 115 × 120 mm with the same opening area. The 160 × 86 mm control beam had a high shear capacity of 2.6% compared to 86 × 160 mm. The inclusion of fibre increased the compressive stiffness of the strut; The beam with fibre and opening size 165 × 170 mm had a shear capacity of 37.8% higher than the beam without fibres. The addition of mesh had a limited increase in shear capacity compared to random fibre mixes; however, the capacity was 21.6% higher than the control mix for a beam with an opening size of 165 × 170mm. Therefore, it is recommended to use recycled waste tyre steel fibres to improve the shear capacity of the deep concrete beam and less application of shear bars.

Experimental investigation of vibration-induced shear resistance reduction in sheared granular soils

To investigate the characteristics of vibration-induced shear resistance reduction (ViSRR) in granular soils, laboratory tests were performed using a modified triaxial apparatus. Monotonic loading and vibration with controlled frequency and acceleration amplitude were superimposed to soil specimens under drained conditions. Tests were conducted for dry and saturated specimens at relative densities of Dr = 35% and 70%. The tests revealed that superimposed vibration causes a reduction of shear resistance in addition to an additional volume change of the specimen. After the termination of vibration, the shear resistance was found to be recovered as the monotonic shearing continued. It was confirmed that the shear resistance reduction was not caused by vibration-induced variation of excess pore pressure in the specimen. For high-frequency vibration with frequency varying between 60 and 120 Hz, the relative shear resistance loss tended to increase linearly with the peak acceleration. Based on the test results, the concept of “vibro-critical state” is proposed to describe the ViSRR of granular soil subjected to monotonic shear and vibration simultaneously.

A Modified Triaxial Apparatus for Soils under High-Frequency, Low-Amplitude Vibrations

Abstract A modified triaxial apparatus was developed to explore the behavior of cohesionless soil subjected to high-frequency, low-amplitude vibrations, such as those induced by high-speed trains. It was based on a conventional Bishop-type triaxial apparatus to utilize its existing static loading module. The major modification was an added dynamic loading module with a low-inertia linear voice coil actuator mounted coaxially with the vertical loading rod. Through a signal generator and an amplifier connected to the voice coil actuator, a vibration input with wide range of frequencies and amplitudes could be superimposed to a monotonic loading process. A series of tests under different conditions were performed to demonstrate the effectiveness and performance of the modified triaxial apparatus, with the focus being placed on the reduction of shear resistance and accumulative deformation of sand induced by high-frequency, low-amplitude vibrations.

Development of Shear Resistance Formula for the Y-Type Perfobond Rib Shear Connector Considering Probabilistic Characteristics

A design shear resistance formula for Y-type perfobond rib shear connectors is proposed with the various reduction factors, which can be selected depending on the target safety level. The nominal shear resistance formula is improved based on the systematic sensitivity analysis as well as the regression fit test based on 84 push-out test results, including 15 additional push-out tests to extend the application ranges and reduce the estimation errors, compared to the formula proposed in previous studies. Some design variables are additionally included in the proposed design formula: the yield strengths of rebar and rib plate. The basic design variables in the proposed design formula are (1) number of ribs and transverse rebars, (2) concrete compressive strength, (3) rebar diameter and yield strength, and (4) rib thickness, width, height, and yield strength. The application ranges of the basic design variables are recommended for the proposed design formula. The various shear resistance reduction factors are proposed based on the probabilistic ultimate shear resistance model of Y-type perfobond rib shear connectors. The proposed procedure may be recommended to develop the design formula for shear connectors with various shapes.

Experimental study on demountable steel-concrete connectors subjected to combined shear and tension

Composite beams are being used increasingly in construction due to their benefits over beams consisting of the steel component alone. In some applications such as in composite coupling beams and infill walls, steel-concrete connectors must resist uplift forces in addition to shear forces. Therefore, there is a need to carry out experimental testing to investigate the performance of steel-concrete connectors under combined loading. Furthermore, the separation of the steel and concrete components is a destructive activity and requires remelting of the steel component if it is to be reused. Remelting requires energy that usually comes from unsustainable resources. Hence, research has been carried out in this paper on demountable steel-concrete connectors as they allow demounting and easy separation of the steel and concrete components and reuse.The performance of three types of steel-concrete connectors subjected to combined shear and tensile loading was investigated experimentally. A pull-out test was carried out to determine the tensile resistance of each type of steel-concrete connector. This was followed by a series of modified push tests to determine the interaction between shear and tension loading. Tensile resistance which had been determined from pull-out tests was applied in increments of 25% to each group followed by shear loading until failure of the steel-concrete connector was observed.Based on the experimental investigation carried out, significant reduction in shear resistance was observed when tension was applied. The results are also compared with existing relationships for headed studs under combined shear and tensile loading to determine which relationship is most reliable in predicting the shear-tension resistance interaction of demountable steel-concrete connectors.

Analysis of sequential active and passive arching in granular soils

Arching in soils has received great attention due to its significance on the soil–underground structure interaction. The state of stress on underground structures as a result of cycles of active and passive arching was neither explored nor systematically assessed. In the present study, comprehensive investigation was carried out to examine: i. the effects of displacement direction to induce active or passive arching, ii. the behaviour of subsequent arching, iii. the effect of magnitude of initial displacement on the formation of arching and iv. the influence of soil height on sequential active and passive arching. The results showed that alternating the displacement of the underground inclusion exacerbated the formation of active and passive arching leading to a substantial reduction in shear resistance and stress redistribution. It is noted that sequentially alternating displacement of the underground inclusion was detrimental to the formation of full active and passive arches irrespective of the burial height.

Evaluation of the effective parameters on shear resistance of interface in a geocomposite-reinforced pavement

Application of geosynthetics is known as an important way to reduce and delay emergence of reflective cracks. However, reliance on these materials can have some disadvantages, including reduction of shear resistance in the interface between two HMA layers, along with emergence of some defects in areas on which vehicles brake, accelerate or turn. A large number of parameters affect the interlayer shear resistance. In this research activity, a double-shear device has been developed and evaluated in order to measure shear resistance between layers in the interface zone. The device is equipped by a system for application and control of normal compressive and tensile loading. In this research, using the L16 (2 × 2–4 × 4) orthogonal array, the factors that are most influential on the shear resistance of the interlayer zone reinforced by geocomposite are evaluated. Temperature, with effectiveness 2.4 times greater than that of the other parameters, the effect of which is relatively uniform, is found to be the most relevant parameter, followed by the tack-coat application rate. The findings indicate that the shear loading rate and geocomposite grid size have the next most significant contribution to the maximum shear resistance, both with and without application of normal load.

Deslizamiento Las Torres, volcán Irazú, Costa Rica: definición de su volumen y su dirección preferencial de movimiento

Se ha efectuado un estudio de inestabilidad de laderas en el sector oeste del volcán Irazú, el cual comprende la definición de un marco geomorfológico, la aplicación de la técnica de elementos finitos conocida como reducción de la resistencia al corte, para analizar la estabilidad del sector definido como en proceso de desestabilización y la definición del volumen de material potencialmente deslizable. El Deslizamiento Activo Río Sucio Oeste (DARSO) se identificó como el único deslizamiento activo en el sector estudiado. Adicionalmente, se ha establecido que el Deslizamiento Inactivo Retes (DIR) muestra evidencias de reactivación en el sector de su escarpe principal. Por otra parte, no se espera que la geoforma DSPD presente un movimiento hacia el suroeste en el futuro y las deformaciones mostradas por el modelo de un desprendimiento hacia el noroeste se tornan significativas una vez que a las propiedades de resistencia al corte se les aplica un factor de reducción de 1,30; desarrollándose el colapso de la ladera en una dirección de deslizamiento hacia el noroeste. Si se considera que el factor de seguridad es de alrededor de 1,30, se debe contar con un factor de disparo para que el deslizamiento se desarrolle. Finalmente, el volumen del deslizamiento se estima en 7 millones de metros cúbicos.

Effect of vibration of flexible transducer on shear resistance of scaling in tunnel drainage

Through a series of laboratory tests, an investigation was conducted into the reduction of shear resistance of scale in tunnel drainage through the use of wave energy. A flexible transducer was used to generate vibration and emitted it through a polyvinylidene fluoride polymer film as various frequencies. Tests were conducted using specially designed and fabricated equipment. The results of the study showed a significant decrease in shear resistance when sonication was applied. The degree of reduction varied by frequency. Using the test results, we discuss the potential development of a new maintenance system method for drainage.

The mechanisms and characteristics of a complex rock-debris avalanche at the Nigeria–Cameroon border, West Africa

We describe a rock-debris avalanche which occurred on steep, symmetrical ridges resulting from fracture-controlled erosion in the valley. The fractures were partially filled with clayey materials, probably derived from the weathering of feldspar. Major fault lines trending N–S were located less than 7km from the landslide location. Exposed sections revealed that the basal rock units were migmatites and gneisses, while the upper section consisted of porphyritic granites. A failure of the residual clay-rich soil, composed of visible crystals of feldspar and mica, is thought to have triggered a long chain of events that led to the development of a rock-debris avalanche, which diverted the course of the rivers in the valley. The area was characterised by a shallow water table in the dry season (2 to 3m) and this might have facilitated the formation of a slip surface at the regolith–rock interface. Field observations and laboratory analysis showed that the regolith probably failed first because of high pore pressure build-up and rapid reduction in shear resistance; this then triggered the failure of the fractured rock units. The slope movement was perpendicular to the foliation of the gneissic rocks, which probably contributed to landslide mobility. Of interest was that changing saturation level at constant relative density of about 32% resulted in either complete or limited liquefaction, indicating that the mechanism of failure depended on the moisture content of the regolith.