Estimating the index properties of deteriorated carbonate rocks due to freeze–thaw and thermal shock weathering

Laboratory tests were conducted on 12 different carbonate rocks to investigate index properties of deteriorated rocks due to physical weathering. Physical weathering due to freeze–thaw and thermal shock action for 20 cycles, was simulated, following the procedure suggested by standard methods. Index properties, P-wave velocity, uniaxial compressive strength and Schmidt hardness, for the three series of the rock samples were determined for fresh, freeze–thaw and thermal shock conditions. It was found that the index properties of rocks treated with freeze–thaw and thermal shock decrease in varying levels with respect to initial values. A model equation predicting the index properties of rocks due to freeze–thaw and thermal shock treatment was developed by multiple regression analysis of measured data. This model explains decrease in index property of a deteriorated rock depending on its initial property and porosity of rock with the coefficients for a specific index property, given in the paper for the both freeze–thaw and thermal shock treatments. Model was validated by statistical tests. In order to estimate the index property for any cycle of freeze–thaw or thermal shock treatment, this model equation was incorporated into a previously suggested model to eliminate a decay constant required for that model to be determined for a specific rock in the laboratory. So, the final model equation could accurately predict a property of a deteriorated carbonate rock depending on treatment cycle, and initial index property and porosity. This was also proved by comparing the model with compressive strength data of a researcher for freeze–thaw cycles.     

Prediction of cyclic freeze–thaw damage in concrete structures based on response surface method

The initiation and growth process of cyclic ice body in porous systems are affected by thermo-physical and mass transport properties as well as by gradients of temperature and chemical potentials. Furthermore, the diffusivity of deicing chemicals reaches a significantly higher value under cyclic freeze–thaw conditions. Moreover, disintegration of concrete structures is aggravated by marine environments, higher altitudes, and northern areas. A serious concern for concrete engineers is that the property of cyclic freeze–thaw with crack growth and the deterioration, caused by accumulated damages hard to be identified by testing. In order to predict the accumulated damages by cyclic freeze–thaw, an optimized regression analysis by response surface method (RSM) is performed. Such important parameters for cyclic freeze–thaw-deterioration of concrete structures as water to cement ratio, entrained air pores, and the number of cycles of freezing and thawing are used to construct the limit state function of RSM. The regression equation fitted to the important deterioration criteria such as accumulated plastic deformation, relative dynamic modulus and equivalent plastic deformations served as the probabilistic evaluation of the performance to resist the structural degradation. The prediction of relative dynamic modulus and residual strains after 300 cycles of freeze–thaw showed good agreements with the experimental results, showing that the RSM result can be used to predict the probability of failure for the accumulated damage by cyclic freeze–thaw using designer specified critical values. Hence, it is possible to evaluate the life cycle management of concrete structures by the proposed prediction method in consideration of the accumulated damage due to cyclic freeze–thaw.     

Study on the damage propagation of surrounding rock from a cold-region tunnel under freeze–thaw cycle condition

Using an equipment with CT (computerized tomography), the characteristics of damage propagation of rock from a cold-region tunnel were studied under different conditions with freeze–thaw cycles, and the results were described by CT images and CT values. The relationships between damage development and the amount of water-supply, and loading or unloading process were also discussed during the repeated freeze–thaw, respectively, as well as the intensity change; moreover, the rate of breakage was also put forward. It was shown that the CT values and CT images could directly express the damage situation of rock, and the results were expected to provide a referenced basis for numerical computation and the safe running of cold-region tunnel.     

Freeze–thaw and thermal degradation influence on the fracture properties of carbon and glass fiber reinforced polymer concrete

In recent years, it has been found that some concrete structures, even for some high performance concrete and ready mixed concrete under good quality control, start to deteriorate long before reaching their designed service life. Cracks are found after the structure has been completed for a few years, which results in the shortening of service life and lowering in durability. In this paper, the influence on the fracture properties of fiber reinforced polymer concrete, FRPC, subjected to freeze–thaw and thermal degradation, is discussed. The study on the damage influence was conducted using a climate chamber to perform the temperature changes on the single edge notched beams. FRPC specimens were subjected to freeze–thaw and higher temperature cycles and then tested according to RILEM standards. To determine the stress intensity factor, K_Ic, critical crack tip opening displacement CTODc, the Two Parameter Method was used and the fracture energy, G_f of the specimens was calculated to evaluate the fracture properties of FRPC. Three-point bending tests were carried out on notched beams with a clip gauge attached to measure the crack mouth opening displacement CMOD. Polymer concrete was reinforced with short glass and carbon fiber with 1% and 2% in mass respectively, to determine whether the reinforcement increases the performance of the material. The fracture properties of FRPC are reported in such conditions.     

Effect of initial curing on chloride ingress and corrosion resistance characteristics of concretes made with plain and blended cements

This paper reports the results of an experimental study conducted to evaluate the effect of initial curing conditions on the chloride ingress characteristics of concretes made with plain and four different blended cements. In addition, the corrosive behavior of steel bars embedded in plain and blended cement concretes were studied through half-cell potential measurements. A total of ten different concrete mixtures having water–cement (w/c) ratios of 0.65 and 0.45 were cast and tested. Test specimens were subjected to three different initial curing conditions, namely uncontrolled, controlled, and wet before exposure to high chloride environment. The research variables included cement type (i.e., plain and blended cements), w/c ratio, and initial curing condition. The results indicated that the initial curing condition had pronounced effects on the related properties: in particular, the most prominent effects were observed on blended cement concretes, which performed extremely well when initially cured in wet conditions. Inadequate or poor initial curing practice resulted in remarkably lower chloride penetration resistance for both plain and especially blended cement concretes.     

An Investigation into the critical factors affecting the performance of composite controlled permeable formwork liners: Part I – Drainage medium

The critical elements associated with a CPF drainage medium and their associated effects on the near surface performance of vertically cast concrete slabs are the focus of this study. A range of board absorption levels, textured features and texture depth are investigated using a Taguchi orthogonal array approach. A permeable polypropylene filter layer was used in conjunction with the various drainage mediums. Statistical software was utilised to determine significant variables as a function of the near surface performance. The range of tests used to characterise the surface performance of the various drainage mediums include surface roughness, surface hardness, surface tensile strength and water absorption. Results are compared to a control sample which was cast against impermeable plywood formwork. All drainage medium permutations showed similar evidence of water/cement ratio reduction at the near surface region of the concrete slab. Surface quality was analysed using quantitative methods and showed significant improvements for all systems over the control. The results for the systems studied indicate that the features of a drainage medium are not critical to the functionality of a CPF liner to reduce the near surface w/c ratio. In fact, it is indicated that the absence of a drainage medium has the same enhancement in near surface concrete slab properties as that of a complex structure when compared to the control sample.     

Role of overconsolidation on sand–geomembrane interface response and material damage evolution

The behavior of high-density polyethylene (HDPE) reinforcement elements is critical to the overall performance of many geotechnical structures including landfills, retaining walls, embankments, and shallow foundations. The reinforcement elements, which may consist of manufactured sheets or strips, must be properly installed in order to transfer stresses from areas of concentrated loading to reinforcing zones. While attention is given during construction to avoid contact damage of reinforcement elements, the construction process exerts stresses on the reinforcement element that may substantially exceed the stresses acting throughout the structure's service life. This paper examines the influence of overconsolidation of HDPE reinforcement elements on interface performance through examination of its effect on sand–smooth geomembrane interfaces. A range of overconsolidation and operational normal stress values are selected based on conditions typically present in practice. Results show the peak friction coefficient to increase substantially with overconsolidation magnitude while the effect on the residual friction coefficient is minimal. The magnitude of the increase in peak friction coefficient is shown to be dependent on both the damage induced by the smooth geomembrane and the degree to which sand particles adjacent to the interface undergo damage in the form of breakage during shear. The damage induced by the smooth geomembrane and the sand particles are presented in terms of the level of overconsonsolidation, confinement stress during shear, and particle characteristics such as angularity and hardness.     

Evaluation of ground motion scaling methods in soil–structure interaction analysis

Dynamic analysis of structures deals with scaling of ground motions, which is vital for estimation of seismic responses. A major source of variability in seismic responses of structures arises from scaling of ground motions. In this paper, the accuracy of six conventional scaling methods on estimation of engineering demand parameters of soil–structure interacting systems is investigated. Two‐dimensional structural models of 5, 10, and 20 stories shear buildings are studied by using stick models, whereas the underlying soil is modeled using the cone model concept. This research attempts to elucidate the accuracy of considered methods for the evaluation of responses. The results show that a suitable scaling method for a response may differ from one to another in terms of accuracy and efficiency. Copyright © 2012 John Wiley & Sons, Ltd.     

Fire resistance of composite columns with embedded I-section steel — Effects of section size and load level

This paper presents a numerical study on the fire resistance of embedded I-section composite columns designed according to EC4 Pt.1.2. The objective is to examine the effects of cross-sectional dimension and load level on column fire resistance. Four groups of columns consisting of square cross-section are chosen for study. Their cross-sectional dimensions range from 250×250 to 400×250 mm², respectively. These columns are subjected to axial compression forces and four-face uniform heating. Within each group four load levels are studied, viz., 0.2, 0.3, 0.4 and 0.5. Based on numerical analyses, it is found that under high load levels, columns with small cross-sections fail to meet the fire resistance as suggested by EC4 Pt.1.2. To validate and to prove the reliability of the numerical study, four composite columns were tested under transient heating scheme. The experimental results were validated against finite element (hereafter: FE) analyses. FE predictions of both cross-sectional temperature distribution and structural response during heating agreed reasonably well with experimental data. Column failure times are also predicted using a simple method suggested by EC4 Part 1.2. It shows that EC4 predictions agree very closely with the FE predictions.     

Determination of stress–strain relationship of tubular material with hydraulic bulge test

Based on the plastic membrane theory and force equilibrium equations, etc., a unique approach is proposed with the curve fitting of experimental data to determine the stress–strain relationship of a thin-walled tube in hydroforming process (THF). A simple and practical hydraulic bulge test tooling was developed and free-bulged tests were performed on stainless steel and low carbon steel tubes to obtain required experimental deformation data. Finite element (FE) simulations of the free bulges were carried out to verify the approach indirectly. The results indicate that the present approach is accurate and acceptable to define the stress–strain behavior of tubular material, and furthermore, an extended flow stress curve with large strain can be obtained by the approach.     

Coupled flexural–torsional dynamic stiffness matrix of an elastically supported axially loaded beam with shear resistant in‐fill

The dynamic stiffness matrix of an axially loaded elastically supported uniform beam with doubly asymmetric cross‐section that exhibits coupling between flexural and torsional motions is developed and subsequently used to investigate its free vibration characteristics. The beam comprises a thin‐walled outer section that encloses, and works compositely with, a core of shear resistant in‐fill material. The outer layer provides flexure, warping and Saint–Venant rigidity, while the inner layer provides both Saint–Venant and shear rigidity. A three‐parameter Winkler model is used to describe the distributed elastic support. Hamilton's principle is used to derive the partial differential equations governing the free vibration of the beam, together with the associated natural boundary conditions. This gives rise to three coupled equations that are subsequently combined into a single, 12th order, ordinary differential equation. Throughout the process, the uniform distribution of mass in the member is accounted for exactly and thus necessitates the solution of a transcendental eigenvalue problem. This is accomplished using the Wittrick–Williams algorithm, which enables the required natural frequencies to be converged upon to any required accuracy with the certain knowledge that none have been missed. Finally, in order to verify the accuracy of the presented theory, the numerical solutions are given and compared with the results that are available in the literature and finite element solutions using abaqus software. Copyright © 2014 John Wiley & Sons, Ltd.     

A beam model for the flexural–torsional buckling of thin-walled members with some applications

A beam model aimed at describing the flexural–torsional buckling of thin-walled members with non-symmetric cross-sections is presented. Two beam axes are introduced, and strain is defined with respect to both. The shearing strain between the cross-section and one of the two axes is assumed to vanish; the warping is supposed to be linear in the twist. Non-linear hyperelastic constitutive relations are introduced; by means of standard localization and static perturbation techniques, the field equations describing the flexural–torsional buckling are obtained. One benchmark example is given and some numerical values of the critical load for various warping constraints at the beam ends are provided.     

Alternative solution for kinematic interaction problem of soil–structure systems with embedded foundation

An effective procedure to incorporate kinematic interaction (KI) aspects in seismic analysis of soil–structures systems was presented. In this regard, first, the effect of KI on the structural response was investigated with special focus on the role of rocking component of foundation input motion (FIM). This was performed parametrically for a wide range of selected nondimensional parameters, which well define the introduced simplified soil–structure model. It was observed that ignoring the effect of rocking input motion may introduce errors, which can be on the unsafe side especially for slender structures with large embedment ratios. On the other hand, it was known that introducing the rocking input motion makes the problem too complicated to be addressed by simplified guidelines suitable for seismic codes or practicing engineers. As an alternative solution, a modified translational input motion was introduced, which can replace both translational and rotational components of FIM. This modified input motion, which was referred to as the net horizontal (NH) FIM in this article, was generated such that the roof displacement of the soil–structure system to this motion is identical to that of the same model subject to the multicomponent FIM resulted by KI. The applicability of the proposed procedure was then examined for a wide range of soil–structure systems subjected to a couple of real ground motions. Copyright © 2010 John Wiley & Sons, Ltd.     

Effects of soil on the energy response of equipment–structure systems with different connection types between the equipment and structure

In equipment–structure systems, the soil–structure interaction and connection types between the equipment and structure significantly affect the seismic response. To understand this effect, in this study, the motion equation of an equipment–structure–soil system was derived, and energy balance equations for each part of the coupled system were obtained. Further, the effects of the soil on the energy response were analyzed based on the results of shaking table tests of an equipment–structure system and real‐time substructure shaking table tests of equipment–structure–soil systems with different connection types. The energy response of the equipment–structure system with a rigid ground was compared with that of the equipment–structure–soil systems. The analysis results showed that the energy response of the equipment–structure–soil system with different connections was quite different from that of the system with a rigid ground. The soil decreased the total energy input to the equipment and structure and significantly changed the time distribution characteristics of the input energy. Additionally, the soil weakened the energy consumption of the connections. Therefore, the influence of the soil should be considered in the design of equipment–structure systems with connections.     

Multiobjective optimal placement of active tendons to control irregular multistory buildings with soil–structure interaction

In recent decades, many researchers have conducted research studies on structural control to improve the safety and serviceability of high‐rise buildings against earthquakes and strong winds. On the other hand, applying active control systems and controlling strategies in buildings are costly process, and it is necessary to reduce the number of controllers. In this paper, a multiobjective genetic algorithm is proposed to optimize the placement of active tendons in a 2D shear frame and a 3D irregular building considering soil–structure interaction effect to reduce active control cost and response of structures at the same time. For multiobjective optimization, multiobjective genetic algorithm of the MATLAB toolbox is used to find a set of Pareto optimal solutions for a multiobjective minimization. The results indicate that the method is capable of finding the number and location of the required active tendons in both 2D shear frame and 3D irregular building with 10 and 20 stories while the base shear of structure is minimized. The specific advantage of the employed algorithms is to reduce the number of mounted active tendons approximately by 50%.     

Critical load of a bilayered orthotropic elastic–plastic conical shell with the change of the shell basic surface location

The paper presents the derivation of stability equations and the comparison of critical loads for an orthotropic elastic–plastic conical shell with proper location of the shell basic surface. Prandtl–Reuss plastic flow theory is accepted in the analysis. To derive the stability equations the variational method was accepted and Ritz method was used to solve the equations. Numerical results were obtained by the use of a special iterative algorithm of the elastic–plastic analysis implemented on the PC.     

Coupled‐two‐beam discrete model for dynamic analysis of tall buildings with tuned mass dampers including soil–structure interaction

An equivalent coupled‐two‐beam discrete model is developed for time‐domain dynamic analysis of high‐rise buildings with flexible base and carrying any number of tuned mass dampers (TMDs). The equivalent model consists of a flexural cantilever beam and a shear cantilever beam connected in parallel by a finite number of axially rigid members that allows the consideration of intermediate modes of lateral deformation. The equivalent model is applied to a shear wall–frame building located in the Valley of Mexico, where the effects of soil–structure interaction (SSI) are important. The effects of SSI and TMDs on the dynamic properties of the shear wall–frame building are shown considering four types of soil (hard rock, dense soil, stiff soil, and soft soil) and two passive damping systems: a single TMD on its top (1‐TMD) and five uniformly distributed TMDs (5‐TMD). The results showed a great effectiveness of the TMDs to reduce the lateral seismic response and along‐wind response of the shear wall–frame building for all types of soils. Generally speaking, the dynamic response increases as the flexibility of the foundation increases.     

Design and specification compilation of a modular‐prefabricated high‐rise steel frame structure with diagonal braces part II: Elastic–plastic time‐history analysis and joint design

The use of modular‐prefabricated steel structures has distinct advantages, such as rapid construction, industrial production, and environmental protection. Although this type of structure has been extensively employed around the world, it is primarily used for low‐rise buildings; its application in high‐rise buildings is limited. This paper proposes a new type of modular‐prefabricated high‐rise steel frame structure with diagonal braces. An elastic–plastic time‐history analysis of a 30‐storey building during rare earthquakes was performed. The base shear, storey drift, stress, damage characteristics, and other performances of the structure were investigated. According to the mechanism analysis, finite element simulation, and model test, the formulas for the elastic and elastic–plastic design of the truss–column connection, column–column flange connection, and diagonal brace–truss connection are proposed in this paper. The control parameters for the structural design are also discussed. This study provides an important reference for the research and design of this type of modular‐prefabricated high‐rise steel structure. The design method has been compiled into a design specification named Technical Specifications for Prefabricated Steel Frame Structure with Diagonal Bracing Joints, which is unique for this type of structure.     

Interaction of shotcrete with rock and rock bolts—A numerical study

The shotcrete–rock interaction is very complex and is influenced by a number of factors. The influence of the following factors was investigated by a series of numerical analyses: the surface roughness of the opening, the rock strength and Young's modulus, the discontinuities, the extent and properties of the excavated disturbed zone, the mechanical properties of the interface between shotcrete and rock, and the thickness of the shotcrete lining and the rock bolts. The study was carried out as a sensitivity analysis. The results showed that the rock strength and the surface roughness had significant impact on the number of failures at the rock–shotcrete interface and in the shotcrete lining. Furthermore, the behaviour of the lining is sensitive to small amplitudes of the surface roughness. In all the cases investigated, a high interface strength was favourable. The results indicate that if a thick shotcrete lining is dependent on the bond strength. The benefit of using a thicker lining can be doubtful. The analyses showed that for an uneven surface the extent of the EDZ had a minor effect on the behaviour of the shotcrete lining. Furthermore, if rock bolts were installed at the apex of the protrusion instead of at the depression, the number of failures decreased both at the interface and in the lining.     

Dynamic experimental and numerical study of double beam–column joints in modern traditional‐style steel buildings with viscous damper

Modern traditional‐style steel (MTS) structure is an innovative architecture structure that is widely used in China. This paper explores the possibility of using viscous damper, which can be conveniently installed between beam and column, to replace “sparrow brace” at beam–column joints to improve its seismic capability. Three 1/2.6 scaled MTS double beam–column joints, one without viscous damper and two with viscous damper, were fabricated and tested under dynamic cyclic loading. The results indicated that the primary failure modes were cracking of base metal and local bucking at the beam ends. The hysteretic curve of specimens with viscous dampers was more plump than the common specimen without viscous dampers, indicating better energy dissipation capacity. The displacement ductility ratio was about 1.79–1.96, indicating the viscous damper has little effect on the ductility, whereas in plastic stage, the energy dissipation of specimens and viscous damper increased rapidly, indicating great energy dissipating function of viscous damper. Meanwhile, the results also proved that finite element analysis may stimulate and predict the mechanical behavior of MTS double beam joints with viscous dampers.