Shear Strength Reduction Factor Research Articles

Mechanical properties and energy evolution of drilling shaft lining concrete under hydro-mechanical coupling

As the drilling shafts in the western mines of China are going to cross the deep water-rich and weakly cemented rock layer, investigating the mechanical properties and energy evolution of shaft lining concrete within the context of hydro-mechanical coupling is crucial. In this study, concrete compression tests were conducted using the TAW-2000 rock testing machine. The concrete damage and rupture mechanisms were analyzed using a combination of mercury intrusion porosimetry and scanning electron microscopy. Moreover, a thorough investigation of the energy evolution throughout the concrete stress-strain process was conducted. The key results include the following: (1) The formulation of the normalized decay equation for the characteristic strength of concrete under hydraulic coupling was derived by computing the ratio of pore water pressure to confining pressure as the characteristic parameter. (2) The effective shear strength reduction factor characterizing the impact of water pressure on the effective shear stress with a correlation coefficient greater than 0.999. (3) The pore water pressure adversely affected the pore size distribution within the concrete, enhancing the connectivity between pores. (4) The total input energy, elastic energy, and dissipated energy were positively related to the confining pressure and negatively related to the pore water pressure. The energy consumption ratio served as a tentative criterion for assessing the strength failure of the shaft lining concrete, which is considered to be in a critically stable state when the energy consumption ratio is 1. These results provided valuable insights into the damage laws and energy-driven mechanisms of shaft-lining concrete under hydraulic coupling conditions.

Shear strength reduction factor used in critical state models with hardening

The slope stability analyses are important to predict environmental, financial, and human life impacts. The Limit Equilibrium Method (LEM) is commonly used to estimate a slope’s Safety Factor (SF). However, the Finite Element Method (FEM) is increasingly applied to slope stability analyses, using different approaches, among which the technique of Shear Strength Reduction (SSR) is commonly used in perfectly plastic elastic models. The objective of this study is to present a discussion about these two methodologies, using critical state models with or without hardening will be used to model the stress-strain behavior of the soil mass. The results obtained in the case study presented, using LEM and FEM considering critical state models with and without hardening are consistent and allowed verifying the stability condition of the slope. Also, the reduction factors are smaller when compared to the results using perfectly plastic elastic models.

Effect of Inclined Tension Crack on Rock Slope Stability by SSR Technique

The tension cracks and joints in rock or soil slopes affect their failure stability. Prediction of rock or soil slope failure is one of the most challenging tasks in the earth sciences. The actual slopes consist of inhomogeneous materials, complex morphology, and erratic joints. Most studies concerning the failure of rock slopes primarily focused on determining Factor of Safety (FoS) and Critical Slip Surface (CSS). In this article, the effect of inclined tension crack on a rock slope failure is studied numerically with Shear Strength Reduction Factor (SRF) method. An inclined Tension Crack (TC) influences the magnitude and location of the rock slope’s Critical Shear Strength Reduction Factor (CSRF). Certainly, inclined cracks are more prone to cause the failure of the slope than the vertical TC. Yet, all tension cracks do not lead to failure of the slope mass. The effect of the crest distance of the tension crack is also investigated. The numerical results do not show any significant change in the magnitude of CSRF unless the tip of the TC is very near to the crest of the slope. A TC is also replaced with a joint, and the results differ from the corresponding TC. These results are discussed regarding shear stress and Critical Slip Surface (CSS).

Performance of grouped stud connectors in precast steel-UHPC composite bridges under combined shear and tension loads

Ultra-high performance concrete (UHPC) becomes an innovative resolution for facilitating the construction and structural performance of prefabricated bridges. Head stud shear connectors are commonly applied in prefabricated steel–concrete composite bridges and can withstand uplift forces as well as shear forces. In this paper, six standard push-out tests (SP-Test) and ten modified push-out tests (MP-Test) are prepared and tested. In the MP-Test, stud connectors are subjected to shear and tensile forces simultaneously. The stud diameter, stud aspect ratio and the ratio of tension to shear are considered for their effects on shear resistance, shear stiffness and ductility. Besides, the finite element (FE) analysis and parametric analysis are conducted to further investigate the behavior of stud connectors under combined loads. The formulas for predicting the shear-tension interaction strength and shear resistance of stud connectors in UHPC under combined loads are proposed. The results show that the stud connectors exhibit both shear and tension failure characteristics under combined loads. The lower ratio of tension to shear has less effect on the shear resistance and ductility. Meanwhile, the stud aspect ratio is positively related to shear resistance and ductility but has no effect on shear stiffness under combined loads. As the ratio of tension to shear increases, a considerable reduction is observed in the shear resistance and relative slip as well as shear stiffness of stud connectors. However, the attenuation effect of tensile stress on the shear strength of studs can be neglected when the tensile shear ratio is less than 0.17. The unevenness of the force on single stud in stud connectors can be ignored and excessive strength of UHPC has limited effect on improving the strength of studs under combined shear and tension loads. The proposed shear strength reduction factor takes into account the ratio of tension to shear and gives more reasonable predictions of shear resistance under combined loads. Besides, compared with other available equations, the proposed shear-tension interaction model predicts the interaction strength more accurately.

Shear behavior of steel plate girders considering variations in geometrical properties

This paper presents equations to determine the ultimate shear strength reduction factor of web plate in steel plate girders due to initial imperfection. The proposed equations are based on a parametric study of shear behavior of steel plate girders considering variation in geometrical properties of the section. 112 models with various initial imperfections, flange-to-web stiffness ratios, and web slenderness were analyzed using finite element software ABAQUS. Both geometric and material nonlinearity have been considered. According to the results, the ultimate shear strength proposed by AISC code is conservatively less than the obtained results by FEM, especially for slender plates; the difference between these two values could reach up to 60% in some cases. That is while, for compact and non-compact web plates, maximum difference is about 10%. Furthermore, it is observed that AISC elastic shear buckling strength is conservatively less than the results derived from FEM. This difference in slender and compact web plates reaches to almost 40% and 20%, respectively. This study reveals that the initial geometrical imperfection is an effective parameter on the shear strength of web plates. According to the results, the sensitivity of girders to initial imperfection is greater in non-compact-web girders than the slender or compact ones, and the maximum shear strength reduction is observed about 23% for maximum allowable imperfection as recommended in part1–5 of EC3. Based on the obtained results, a maximum permissible construction tolerance is proposed as well.

Shear Strength Reduction Factor of Prestressed Hollow-Core Slab Units Based on the Reliability Approach

This study investigated the shear design equations for prestressed hollow-core (PHC) slabs and examined the suitability of strength reduction factors based on the structural reliability theory. The reliability indexes were calculated for the shear strength equations of PHC slabs specified in several national design codes and those proposed in previous studies. In addition, the appropriate strength reduction factors for the shear strength equations to ensure the target reliability index were calculated. The results of the reliability index analysis on the ACI318-08 equation showed that the shear strengths of the members with the heights of more than 315 mm were evaluated to be excessively safe, whereas some members with low depths did not satisfy the target reliability index.

Assessing reduction in concrete shear strength contribution

Design codes use a strength reduction factor that is less than unity. This factor reflects the degree of uncertainty associated with the probability of under-strength members and inaccuracies in the design equations, the importance of the member in the entire structure and the behaviour of a member at ultimate load. A failure probability based on a second moment probabilistic analysis procedure is used in this study to compute the strength reduction factor in predicting the contribution of concrete to shear strength of reinforced-concrete beams according to the American Concrete Institute code ACI 318. For different coefficients of variation of concrete and failure probabilities, the shear strength reduction factor is investigated using experimental studies available in the literature. It is assumed that the random variables are statistically independent, and the correlation effects are not taken into account. It is found that a strength reduction factor of 0·75 for shear is valid in design according to ACI 318 for a coefficient of variation of concrete compressive strength of 0·18 and a failure probability of 10−5.

Progressive failure processes of reinforced slopes based on general particle dynamic method

In order to resolve grid distortions in finite element method (FEM), the meshless numerical method which is called general particle dynamics (GPD) was presented to simulate the large deformation and failure of geomaterials. The Mohr-Coulomb strength criterion was implemented into the code to describe the elasto-brittle behaviours of geomaterials while the solid-structure (reinforcing pile) interaction was simulated as an elasto-brittle material. The Weibull statistical approach was applied to describing the heterogeneity of geomaterials. As an application of general particle dynamics to slopes, the interaction between the slopes and the reinforcing pile was modelled. The contact between the geomaterials and the reinforcing pile was modelled by using the coupling condition associated with a Lennard-Jones repulsive force. The safety factor, corresponding to the minimum shear strength reduction factor “R”, was obtained, and the slip surface of the slope was determined. The numerical results are in good agreement with those obtained from limit equilibrium method and finite element method. It indicates that the proposed geomaterial-structure interaction algorithm works well in the GPD framework.

Shear Capacity of Steel Plates with a Square Opening

Steel plate elements are frequently encountered in structural applications, where thin plates are susceptible for local buckling at low loads, while thick plates may reach their strength limit. An opening of any size and shape on such structural plates may significantly affect the stiffness, strength, and the failure characteristic of the entire plate. The objective of this study is to quantify the shear capacity of plates containing a centrally placed square opening. The finite element method based numerical investigation considered the behavior of simply-supported rectangular steel plates, with and without a square opening and subjected to in-plane shear loading, experiencing buckling, post-buckling, and yielding until failure. The model employed representative material model, initial geometric imperfections and large deflection analysis. The investigation established the shear strength reduction factors due to opening of different parametric dimensions, and compared such results with the reduction factors based on the current cold-formed steel design code provisions. This paper establishes an enhanced shear strength reduction factor design equation, incorporating the impact of a centrally located square opening, for the shear capacity of un-stiffened steel plates.

Residual shear strength of steel plate girder due to web local corrosion

Corrosion damage around the supports of steel plate bridges due to high humidity and depositions as well as rainwater and antifreeze penetration into drainage type expansion joints have been frequently reported. However, the residual shear buckling strengths and behaviors have not been sufficiently evaluated and its evaluation method has not been clearly established. Therefore, in this study, the shear buckling failure modes of web panels with local corrosion were numerically examined from their post-buckling behaviors as well as their shear buckling behaviors. Their shear buckling values were quantitatively evaluated from nonlinear FE analyses model by varying the corrosion conditions and geometrical conditions of web panels. In addition, the FE analysis results were compared with values calculated by a theoretical equation and design specifications. A residual shear strength reduction factor that could be used to estimate the residual shear strength of the plate girder with local corrosion was presented from the relationships between the residual shear strength and the corroded web volume.

An Approach for Landslide Stability Evaluation by Numerical Method

For numerical simulation, the shear strength reduction technique (SSRT) is often used to evaluate slope or landslide stability. According to numerical computation results of slopes or landslides analyzed by SSRT, it can be found that with increase of the shear strength reduction factor, some of the soil elements will yield gradually to form a connected plastic zone, which is the potential slip surface of the slope or landslide. In view of the plastic resistance of soils, formation of the connected plastic zone does not always indicate that the landslide is about to failure. Other auxiliary criterion is necessary to predict whether a slope or landslide is in a critical state or not. Here, difference of the incremental percent of horizontal displacement of the outcropping slip surface node is regarded as the auxiliary indicator to distinguish the critical state of slopes or landslides after formation of the potential slip surface. With the ideas mentioned above, stability of a fossil landslide, Xietan landslide has been analyzed for the natural and the long-term reservoir water level conditions. Factors of safety of Xietan landslide by the numerical method have been compared with that by the limit equilibrium method, which indicates that the method used here for evaluating stability of Xietan landslide is feasible. Because numerical method has more advantages over the limit equilibrium method, the approach for evaluating stability of landslide here can be applied to more complicated or three-dimensional landslides or slopes further.

개구부를 갖는 철근콘크리트 전단벽의 전단강도 저감률

리모델링에는 여러 형태가 있을 수 있다. 그 중 건축주나 리모델링 수행자가 선호하는 방법이 두 개의 주거공간을 하나로 만들어 평면 확장을 목표로 하는 세대 병합형 리모델링이다. 그러나 이러한 방법을 현재 국내에서 리모델링 대상이 되고 있는 벽식 구조의 아파트에 적용할 경우 주요 횡력 저항 요소인 전단벽에 큰 손상을 가하게 될 수 있다. 그러나 아직 이러한 주요 구조 부재인 철근콘크리트 전단벽에 개구부가 발생할 경우의 명확한 손상 정도를 정의해주는 연구는 진행되고 있지 않은 실정이다. 현행 ACI 기준은 이러한 철근콘크리트 전단벽 내의 개구부에 대한 명확한 고려 방안을 제시하지 않고 있다. 반면 AIJ 기준은 철근콘크리트 전단벽 내부의 벽체에 대한 고려 방안으로 강도 저감률 γ를 제시하고 있다. 그러나 이 강도 저감률은 탄성 판 이론으로부터 제시된 것으로 철근콘크리트 부재에 있어서의 강도 저감률을 제대로 표현하지 못하고 있는 실정이다. 그러므로 이 연구에서는 AIJ에서 제시하고 있는 강도 저감률 γ에 대하여 현재까지 진행되었던 실험 결과에 대한 통계적 분석과 유한요소해석을 통한 변수 분석을 통해 개구부에 의한 강도 저감률에 대한 연구를 수행하였다. 통계적 분석 결과 현재 제시되어 있는 강도 저감률은 개구부의 벽체면적에 대한 비율만을 변수로 설정하여 그 저감률이 실험 결과보다 크게 나타나고 있었다. 또한 개구부의 형상비를 면적과 통합적으로 고려하며 철근비에 대한 고려를 하지 못하는 것으로 나타났다. 이에, 기존의 실험 결과와 이를 토대로한 유한요소해석을 통한 변수분석을 수행하여 새로운 강도 저감률을 제안하였다.

Slope stability analysis by strength reduction

Keywords: embankments ; landslides ; limit state design analysis ; numerical modelling and analysis ; plasticity ; slopes ... Show All

Stability of embankment on clay : Hamel, JV Discussion of paper by Wu et al, Sept. 1975 1T, 2R J. Geotech. Engng Div. ASCE, V102, GT5, 1976, P574–576

Comments are made on the possible role of residual strength in effective stress analyses of the embankment failure. It is noted that the minimum effective shear strength likely to occur laong structural discontinuities or progressively developed failure surfaces in clay is the residual strength. The residual friction angle (14 deg.) determined by the authors for slickensides in the foundation is used to estimate safety factors for the three cross sections. Details of the estimation procedure are described, and the estimated safety factors are tabulated. Previous work is quoted that pointed out that stability of embankments on slightly overconsolidated highly plastic clay foundations is generally overestimated by both total and effective stress analyses using shear strengths from conventional laboratory tests. It was proposed that a shear strength reduction factor be used to account for progressive failure of foundation behavior which reduce field mobilized shear strengths. Later studies have shown that rsidual or near-residual shear strengths are mobilized as described.