The bearing strength of steel coupling beam-reinforced concrete shear wall connections

Increasingly, engineers are designing hybrid and mixed building systems of structural steel and reinforced concrete to produce more efficient structures than can be realized using either material alone. In particular, hybrid coupled shear wall of them are known to be efficient lateral load resisting system. However, due to lack of information, current design equations to compute the bearing strength of steel coupling beam–wall connections in a hybrid coupled shear walls are tacit about cases in which the beams have connection details to the walls that include stud bolts and horizontal ties in hybrid coupled shear walls. There were carried out experimental and analytical studies on steel coupling beam–wall connections in a hybrid wall system. Experimental study was carried out to verify the bearing strength of steel coupling beam–wall connections. The test variables included the reinforcement details that confer a ductile behavior on the steel coupling beam–wall connection, i.e., the stud bolts and the horizontal ties in the steel coupling beam–wall connections. The equations proposed in this study to predict strength for steel coupling beam-reinforced concrete shear wall connections were in good agreement with both our test results and other test data from the literature.     

Study on reactor building structure using ultrahigh strength materials

This study was promoted to realize the optimal nuclear reactor building structure of the future. As the first step, the study regarding ultrahigh strength reinforced-concrete (RC) shear walls was positively verified. The tests conducted were relevant to ultrahigh strength concrete material tests, pure shear tests of RC flat panels, bending shear tests and simulation analyses of RC shear walls, S-joint tests and mixed-structure tests. From the results of this study, it was verified that mixed structures using ultrahigh strength material can be realized.     

Failure and fracturing analysis of concrete structures

Some aspects of fracture analysis of concrete structures are discussed in this article. In particular it is shown that when localized failure occurs (by macrofracture propagation or localization of strain) structural size effects come into play. Mesh dependent finite element solutions are then observed unless size effects are correctly accounted for.Tensile fracture is examined first. The “classical” discrete and smeared crack approaches are reviewed and their extension to nonlinear fracture models like the fictitious crack model and the crack band model is illustrated. The smeared crack approach coupled first with a tensile strength criterion, second with a linear elastic fracture mechanics criterion is then applied to the failure mode analysis of a PCRV.Plastic fracturing with localization into shear bands, strain softening, mesh dependence and its correction are examined next. The use of plasticity for tensile fracture simulation is also discussed.Finally numerical difficulties inherent to the modeling of softening behavior are investigated.     

Seismic behaviour and design of steel coupling beams in a hybrid coupled shear wall systems

The hybrid coupled shear wall system is more efficient and economical than individual structural walls because the steel coupling beams connected shear walls significantly increase the strength, stiffness and energy dissipation capacity of the system. In this study, experimental studies on the steel coupling beam were carried out. The main test variables were the ratios of the coupling beam strength to the connection strength. In addition, the seismic design methods are presented for steel coupling beam–wall connection and shear critical and flexure critical steel coupling beams in hybrid coupled shear wall system consisting of steel coupling beams and reinforced concrete shear walls. Finally, this paper provides background for design guidelines in hybrid coupled shear walls that include steel coupling beam–wall connections and steel coupling beams.     

A simplified model for nonlinear seismic response analysis of equipment cabinets in nuclear power plants

An analytical model is required when the analysis method or the combined analysis and modal testing method is used as an aid to the seismic qualification (SQ) of equipment cabinets within nuclear power industry. This study proposes a simplified and computationally efficient model to represent the nonlinear dynamic behavior of the cabinet during earthquake. The presented model accounts for the softening behavior of the cabinets by incorporating the Duffing's type of restoring force. The characteristic of nonlinear restoring force for the finite element model (FEM) is based on the relationship of stress-strain of the element. Experiments have also been performed on an actual cabinet of nuclear power plant (NPP) to validate the model. The softening or reduction in dynamic stiffness of cabinets with increase in the excitation levels is observed in the experiments. It is also found that material yielding is not a significant source of the nonlinear behavior of the cabinet. The results obtained from the analysis using the proposed model are found to be in good agreement with the experimental results. The proposed model is expected to be useful for the prediction of seismic behavior of cabinets, particularly during the operation, owing to less computational effort required, accurate prediction of softening and no requirement of tests.     

A constitutive model for structural analysis of fusion magnets

A constitutive model to simulate the elastic-plastic and slip actions of fusion magnets under operating or abnormal loads is outlined. To represent the elastic-plastic responses a unified material homogenization procedure based on the existing composite technology was applied to obtain an effective incremental stress-strain relationship for the heterogeneous, laminated magnets. The inter-layer slip behavior of the magnets was represented by a friction-type model from which slip deformation can be calculated for the situation where inter-layer shear stresses exceed the bonding strength of the adhesives. Numerical results of three example problems are presented to demonstrate the utility of the proposed model.     

Sleeve-type expansion anchor behavior in cracked and uncracked concrete

A test was performed to investigate the effect of concrete cracks on the static behavior of sleeve-type expansion anchors, and to confirm the seismic and fatigue resistance capability in cracked concrete. The tensile and shear test was conducted on single anchors with three different anchor diameters. Concrete test specimens are sufficiently large to prevent the effect of the concrete edges on the anchor behavior. The types of failure, the static strength and displacement behavior of the anchors in uncracked and cracked concrete were compared to evaluate the effect of the cracks. The strength reduction rate of the anchors due to the cracks was exhibited almost less than the corresponding value specified in ACI 349-01, APP. B. Through the residual strength tests, the seismic and fatigue resistance capability of the anchors was confirmed in cracked concrete. The characteristics of the anchor shear capacity significantly vary with how the displacement failure criteria are determined.     

Empirical investigation on buckling and post-buckling behaviour of cell liners

In nuclear-related facilities, many concete walls and slabs are lined with thin stainless steel plates in order to insure against the risk of accidental air leakage during a severe earthquake. These liners are forcibly deformed with the deformation of the concrete walls and slabs during an earthquake. The purpose of this paper is to obtain basic empirical data on the shearing behaviour of thin steel plates attached to concrete, especially to understand the relationship between the shear strain of the plate and its lateral displacement, as fundamental research on the safety of lining plates. A new apparatus for measuring the lateral displacement of a lining plate by continuously scanning its surface is tested. The apparatus proves to be quite effective for understanding the buckling wave of the lining plate and the essential behaviour of a thin steel plate attached to a concrete wall subject to a shear force is clarified.     

Reinforced concrete membrane elements subjected to reversed cyclic in-plane shear stress

A macroscopic model has become noticeable instead of a microscopic model by FEM analysis for concrete structures. Among them the model proposed by Vecchio and Collins is considered to be one of the powerful tools because of its rationalility and simplicity. The essential point of this model is a modified compression theory of cracked concrete and the stress-strain relationship for cracked concrete.This paper follows basically Collins' theory but is revised so as to be able to predict the response of reinforced concrete elements subjected to alternate reversed cyclic in-plane shear simulating earthquake forces. The overall characteristics of the new model exist in the tensile residual strains accumulated by cycles in cracked concrete, which is different from the monotonic loading.     

Impact of plastic softening of over-aged CuCrZr alloy heat sink tube on the structural reliability of a plasma-facing component

Precipitation-hardened CuCrZr alloy is used in fusion experiments as heat sink material for water-cooled plasma-facing components. When exposed to long-term high-heat-flux (HHF) plasma operation, CuCrZr will undergo over-ageing and thus plastic softening. In this situation, the softened CuCrZr heat sink tube will suffer from substantial plastic straining and thus fatigue damage in the course of the cyclic HHF loads. In this paper, a computational case study is presented regarding the cyclic plasticity behaviour of the over-aged CuCrZr cooling tube in a water-cooled tungsten mono-block divertor component. Finite element analysis was performed assuming ten typical HHF load cycles and using the Frederick-Armstrong constitutive equation together with corresponding material parameters. It was shown that plastic shakedown and low cycle fatigue (LCF) would be caused in the heat sink tube when softening of CuCrZr should occur. On the other hand, neither elastic shakedown nor cumulative plastic strain (ratchetting) was found. LCF design life of the CuCrZr tube was estimated based on the ITER materials handbook considering both hardened and softened states of CuCrZr. Substantial impact of softening of the CuCrZr alloy on the LCF lifetime of the heat sink tube was demonstrated.     

Seismic fragility of reinforced concrete structures in nuclear facilities

The failure and fragility analyses of reinforced concrete structures and elements in nuclear reactor facilities within the Seismic Safety Margins Research Program (SSMRP) at the Lawrence Livermore National Laboratory are evaluated. Receiving special attention are uncertainties in material modeling, behavior of low shear walls, and seismic risk assessment for nonlinear response. Problems with ductility-based spectral deamplification and prediction of the stiffness of reinforced concrete walls at low stress levels are examined. It is recommended that relatively low damping values be used in connection with ductility-based response reductions and that static nonlinear force-deflection curves be studied for better nonlinear dynamic response predictions.     

Shell finite element of reinforced concrete for internal pressure analysis of nuclear containment building

This paper describes a 9-node degenerated shell finite element (FE), an analysis program developed for ultimate pressure capacity evaluation and nonlinear analysis of a nuclear containment building. The shell FE developed adopts the Reissner-Mindlin (RM) assumptions to consider the degenerated shell solidification technique and the degree of transverse shear strain occurring in the structure. The material model of the concrete determines the level of the concrete stress and strain by using the equivalent stress-equivalent strain relationship. When a crack occurs in the concrete, the material behavior is expressed through the tension stiffening model that takes adhesive stress into account and through the shear transfer mechanism and compressive strength reduction model of the crack plane. In addition, the failure envelope proposed by Niwa is adopted as the crack occurrence criteria for the compression-tension region, and the failure envelope proposed by Yamada is used for the tension-tension region. The performance of the program developed is verified through various numerical examples. The analysis based on the application of the shell FE developed from the results of verified examples produced results similar to the experiment or other analysis results.     

Change in flow stress and ductility of δ-phase Pu-Ga alloys due to self-irradiation damage

An internal state variable model for the mechanical behavior of aged Pu-Ga alloys is developed and used to predict the change of the material with accumulated self-irradiation damage or age. The material model incorporates microstructural data such as the primary irradiation-induced defect density from cascades, the density and average size of helium bubbles, the initial dislocation density, and the initial average segment length of the dislocation density as input parameters, and then evaluates the stress-strain response of a representative volume element of the material. Given this response at a single material point, the deformation behavior of tensile specimens is predicted, and it forecasts increased strength, decreased strain hardening, and more strain localization with aging. Although the material point behavior showed some slight strain softening, this strain softening is expected to be masked by statistical variations of different volume elements and by the strain rate sensitivity of the material. Hence, it is not expected to appear in the stress-strain response of macroscopic tensile specimens, and only the increase in flow stress will be measured.     

Gas leakage rate through reinforced concrete shear walls: Numerical study

Unlined reinforced concrete shear walls are often used as ‘tertiary boundaries’ in the United States Department of Energy (DOE) to house dangerous gases. An unanticipated event, such as an earthquake, may cause gases stored inside the walls to disperse into the environment resulting in excess pollution. To address this concern, in this paper, a methodology to numerically predict the gas leakage rate through these shear walls under lateral loading conditions is proposed. This methodology involves finite element and flow rate analysis. Strain distributions are obtained from the finite element analysis, and then used to simulate the crack characteristics on the concrete specimen. The flow rate through the damaged concrete specimen is then estimated using flow rate formulas available from the literature. Results from an experimental specimen are used to evaluate the methodology, and particularly its robustness in the flow rate estimation.     

A microstatistical model for ductile fracture with rate effects

A micromechanical ductile fracture model was used in a parametric study of void-induced softening. The model describes rate-dependent nucleation and growth of microscopic void size distributions. The Gurson yield surface is used as the threshold condition for viscous void growth. The relative amounts of shear stress and mean stress relaxations due to void nucleation and growth in a material element are found to be strongly dependent on both the material viscosity and the path taken by the material element in stress space. Material elements subjected to uniaxial stress load paths show much less shear strength softening than those subjected to uniaxial strain load paths. Shear strength softening is enhanced by loading rates high enough to activate viscous response. Computational simulations of uniaxial stress and strain tests over a range of strain rate show a complicated interplay of the above factors.     

Modeling of shear wall buildings

Many nuclear power plant buildings, for example, the auxiliary building, have reinforced concrete shear walls as the primary lateral load resisting system. Typically, these walls have low height to length ratio, often less than unity. Such walls exhibit marked shear lag phenomenon which would affect their bending stiffness and the overall stress distribution in the building. The deformation and the stress distribution in walls have been studied which is applicable to both the short and the tall buildings. The behavior of the wall is divided into two parts: the symmetric flange action and the antisymmetric web action. The latter has two parts: the web shear and the web bending. Appropriate stiffness equations have been derived for all the three actions. These actions can be synthesized to solve any nonlineal cross-section. Two specific problems that of lateral and torisonal loadings of a rectangular box have been studied.It is found that in short buildings shear lag plays a very important role. Any beam type formulation which either ignores shear lag or includes it in an idealized form is likely to lead to erroneous results. On the other hand a rigidity type approach with some modifications to the standard procedures would yield nearly accurate answers.     

Prestressed concrete deep slabs with openings

A series of small-scale models of prestressed concrete reactor vessels, with and without perforations in the end slab, were loaded to failure. All vessels failed in shear. The presence of penetrations did not decrease the strength of the end slab. The behavior of the vessels is described. Using a finite-element model, the stress conditions in the end slab at the failure load are evaluated. A method for calculating the shear strength of a deep slab is described. The method consists of three consecutive steps. First, calculate the load at which the inclined crack is initiated. Second, determine the shape of the load-carrying dome that is carved out inside the slab. Third, calculate and evaluate the stress conditions in the dome.