Wall Joints Research Articles

A Fractal Model for the Shear Behaviour of Large-Scale Opened Rock Joints

This paper presents a joint constitutive model that represents the shear behaviour of a large-scale opened rock joint. Evaluation of the degree of opening is made by considering the ratio between the joint wall aperture and the joint amplitude. Scale dependence of the surface roughness is investigated by approximating a natural joint profile to a fractal curve patterned in self-affinity. Developed scaling laws show the slopes of critical waviness and critical unevenness tend to flatten with increased sampling length. Geometrical examination of four 400-mm joint profiles agrees well with the suggested formulations involving multi-order asperities and fractal descriptors. Additionally, a fractal-based formulation is proposed to estimate the peak shear displacements of rock joints at varying scales, which shows a good correlation with experimental data taken from the literature. Parameters involved in the constitutive law can be acquired by inspecting roughness features of sampled rock joints. Thus, the model can be implemented in numerical software for the stability analysis of the rock mass with opened joints.

Joint wall clutter mitigation and data-driven model for through-wall detection

ABSTRACTWall effects such as the strong front wall return and the propagation of the signal as it travels through the wall must be taken into account in through-wall detection. First of all, compensation of through-wall propagation effects such as attenuation and dispersion should be considered in imaging procedure assuming effective removal of the strong front wall return (called wall clutter). However, the wave backscattered from the target behind the wall is usually submerged in the wall clutter. In addition, the wall parameters are unknown in practical situation. Therefore, how to detect a target behind the wall without prior knowledge of wall characteristics is becoming a new challenge that is difficult to solve. In this article, a novel method jointing wall clutter mitigation and data-driven model (DDM) is proposed to address this new challenge. First, the total echo is decomposed into wall, target, and noise subspaces using singular value decomposition (SVD), while the image entropy is introduced as an evaluation criterion for selecting the sub-spaces boundary, and therefore the wall clutter is mitigated. Then, through-wall detection problem is cast as a regression one using DDM model and the regression problem is solved by means of Support Vector Machine (SVM). It is demonstrated that the proposed method can efficiently detect the target behind the wall without prior knowledge of its characteristics.

Equivalent frame analysis for effective wall width of nonplanar beam–wall connections

SummaryShear wall–frame structural systems are the most commonly used structural forms in tall buildings. In this structural system, many nonplanar beam–wall connections are formed by frame beams connecting to a shear wall in their out‐of‐plane direction. Few studies on nonplanar beam–wall joints have been conducted. This paper presents an investigation of the mechanical performance of nonplanar beam–wall joints based on the equivalent frame model assumptions. The concept of the effective wall width is introduced, and an analytical model is derived by considering the rotational stiffness of a beam–wall joint. The proposed effective wall width model is verified by experiments and finite element analyses. Comparison of the proposed model with the existing models shows that all the key design variables that affect the effective wall width in nonplanar beam–wall connections, in particular the cross‐sectional dimensions of beams and shear walls, have been appropriately included in deriving the proposed model based on structural mechanics. The applicability and accuracy are demonstrated by a design example. It is shown that the proposed analytical model of the effective wall width for nonplanar beam–wall connections provides a simple and effective, yet accurate, means of analysis for the coupling effect of nonplanar coupling beams in tall buildings. Copyright © 2016 John Wiley & Sons, Ltd.

Case Study of the Core Structure Succeeding Method for Tall Building Construction

AbstractIn tall building construction, the adoption of the appropriate construction method for the core structure process is critical in terms of both the structural aspect of the building and the schedule estimation. This study introduces a new core structure succeeding construction method (CSSCM) for tall buildings with steel-reinforced concrete structures to address the obstacles of the existing core structure preceding construction method (CSPCM) such as limited workspace, interference between activities, difficulties in wall and slab joint construction, and similar obstacles. The study also shows the technical details and compares the results from the applications of CSPCM and CSSCM to an actual tall building project. The results revealed that this method has potential as a cost-effective construction method for structural frameworks of tall buildings where short cycle times are required. In addition, the method provided stable working environments for the steel erection including outriggers and core...

Effect of Thermal Bridges in Insulated Walls on Air-Conditioning Loads Using Whole Building Energy Analysis

Thermal bridges in building walls are usually caused by mortar joints between insulated building blocks and by the presence of concrete columns and beams within the building envelope. These bridges create an easy path for heat transmission and therefore increase air-conditioning loads. In this study, the effects of mortar joints only on cooling and heating loads in a typical two-story villa in Riyadh are investigated using whole building energy analysis. All loads found in the villa, which broadly include ventilation, transmission, solar and internal loads, are considered with schedules based on local lifestyles. The thermal bridging effect of mortar joints is simulated by reducing wall thermal resistance by a percentage that depends on the bridges to wall area ratio (TB area ratio or Amj/Atot) and the nominal thermal insulation thickness (Lins). These percentage reductions are obtained from a correlation developed by using a rigorous 2D dynamic model of heat transmission through walls with mortar joints. The reduction in thermal resistance is achieved through minor reductions in insulation thickness, thereby keeping the thermal mass of the wall essentially unchanged. Results indicate that yearly and monthly cooling loads increase almost linearly with the thermal bridge to wall area ratio. The increase in the villa’s yearly loads varies from about 3% for Amj/Atot = 0.02 to about 11% for Amj/Atot = 0.08. The monthly increase is not uniform over the year and reaches a maximum in August, where it ranges from 5% for Amj/Atot = 0.02 to 15% for Amj/Atot = 0.08. In winter, results show that yearly heating loads are generally very small compared to cooling loads and that heating is only needed in December, January and February, starting from late night to late morning. Monthly heating loads increase with the thermal bridge area ratio; however, the variation is not as linear as observed in cooling loads. The present results highlight the importance of reducing or eliminating thermal bridging effects resulting from mortar joints in walls by maintaining the continuity of the insulation layer in order to reduce energy consumption in air-conditioned buildings.

EXPERIMENTAL INVESTIGATION OF PRECAST WALL JOINTS BY USING SIFCON

In India, the construction field streams towards the hike with the advent of new innovative technologies. The increase in the quantity of construction seeks the superior quality from the researchers in terms of effective methodologies which reduce the requirement of manpower and material with increased efficiency and pace of construction. One of the most promising solutions for this issue suggested by the researchers is the precast construction. Precast construction entirely restructures the conventional construction process to improve the quality and pace of the construction. The predicaments with precast construction are shrinkage of filling material between the wall which leads to crack formation and also cause leakage of water. The occurrence of shrinkage is initiated and leaded by the compacting or filling problem in filling materials up to ground level due to the use of coarse aggregate and the usage of non flexible and improper bonding of sealant in the wall joints. In order to reduce these structural problems, we investigated the method of SIFCON (slurry infiltrated fibre concrete) with varies mix proportion 1: 1, 1:1.5 and 1:2 with the replacement of coarse aggregate by perlite. The sealant we used is poly sulphide sealant and the watercement ratio of the filling material varies between 0.3 and 0.4. Even though the conventional practical way of using fibres in SIFCON is limited up to 12%, we investigated the usage of fibres up to 20% in this experiment. The results obtained from the experiment shows that the filling material with the cement mortar ratio of 1:1.5 with 5% glass fibre applied in the method of Slurry Infiltrated Fibre Concrete successfully arrests the leakage of water between the wall joints.

Direct force control for human-machine system with friction compensation

Purpose– The purpose of this paper is to present a direct force control which uses two closed-loop controller for one-degree-of-freedom human-machine system to synchronize the human position and machine position, and minimize the human-machine force. In addition, the friction is compensated to promote the performance of the human-machine system.Design/methodology/approach– The dynamic of the human-machine system is mathematically modeled. The control strategy is designed using two closed-loop controllers, including a PID controller and a PI controller. The frictions, which exist in the rotary joint and the hydraulic wall, are compensated separately using the Friedland’s observer and Dahl’s observer.Findings– When human-machine system moves at low velocity, there exists a significant amount of static friction that hinders the system movements. The simulation results show that the system gives a better performance in human-machine position synchronization and human-machine force minimization when the friction is compensated.Research limitations/implications– The acquired results are based on simulation not experiment.Originality/value– This paper is the first to apply the electrohydraulic servo systems to both actuate the human-machine system, and use the direct force control strategy consisting of two closed-loop controllers. It is also the first to compensate the friction both in the robot joint and hydraulic wall.

Investigation of Static and Dynamic Characteristics of Complex Thin-Walled Shell Structure with Cracks

A numerical approach to investigation of static and dynamic characteristics of fuel reservoir and surge-protection capacity with cracks in welded joints of their walls has been proposed. Mathematical modeling of the nonlinear behavior of the complex shell structure has been performed under the action of static vertical loading using the software complex of finite element analysis. The models of cracks with different length within vertical and horizontal welded joints of shell walls have been developed. The influence of cracks on the stress-strain state and stability of the fuel reservoir as well as the surge-protection capacity has been investigated. The dynamic characteristics of the structure have been determined, the influence of cracks on the frequencies and the modes of their natural vibrations has been evaluated.

Geomechanical characterization of Newberry Tuff

In this paper we present the results of a petrophysical and geomechanical characterization program focusing on the rock mechanical properties of welded tuffs from Newberry volcano, Oregon. The rock samples are from drill cores obtained from three wells in the vicinity of the Newberry EGS namely, GEO N-2, GEO N-1, and OXY 72–3. As part of the rock characterization process, petrographic thin sections were prepared and used to describe rock texture and mineralogy. High resolution X-ray CT scanner was also used to provide 3D images of the rock pore structure. Rock porosity and permeability were measured using the gas expansion method and a pulse permeameter, respectively. Triaxial compression tests were performed on the specimens extracted from whole core to determine their Young's modulus, Poisson's ratio, and failure envelopes. In particular, multistage triaxial compression tests were carried out to determine deformation and failure properties, and to establish relationships between petrophysical and mechanical/failure properties. In addition, multistage triaxial shear tests were performed to determine the mechanical properties and shear strengths of the fractures developed in triaxial compression tests. Joint roughness coefficient (JRC) and Joint Wall Compressive Strength (JCS) were obtained through analysis of the shear tests. Joint normal stiffness and shear stiffness were also estimated and it was observed that a higher confining pressure results in higher joint shear stiffness. These studies provide insight into the effects of mineralogy and texture and structure on the strength and deformation properties of the tuff samples tested. Mineral composition and the presence of phenocrysts, argillitic materials, and natural fracture were noted to impact rock mechanical properties. Natural fracture and vein mineralogy also influence fracture development in the samples as well as frictional and shear strength properties of the joints tested. Rock samples with higher clay mineral content were found to be relatively more ductile with minimal increase, or even decrease, in permeability under failure in compression tests. The data set obtained in this study is very useful for stimulation design and interpretation of observed micro-seismicity in relation to permeability enhancement.

High-Tech Solutions for Building Retrofit: Investigation of Window Systems with Vacuum Glazing

The retrofit of the historical building stock has gained significance due to energy efficiency requirements in the building sector. Major attention is drawn to windows as they are typically the building components with the highest heat transfer coefficient of the building envelope. Therefore, vacuum glazing is a potential option for improving the thermal performance of casement windows. In this context, specific considerations regarding building physics and heritage protection regulations are required.The present contribution describes the current progress of the research project VIG-SYS-RENO. New double glazing products with durable vacuum layer are emerging on the market. Such developments can be regarded as a major step toward energy-efficient windows with U-values close to conventional opaque building elements. Small thickness and excellent thermal resistance of vacuum insulation glazing renders it an attractive option in thermal retrofit of historical buildings. Vacuum glazing systems could potentially offer a feasible balance between conservation and thermal performance of windows. However, prior to any application, a set of aspects and potential issues have to be assessed and explored. These include: (i) thermal bridging effects in different joint positions, for instance the glass edge seal and the frame & wall joint; (ii) the positioning of tight layers in composite or casement windows; (iii) aspects of structural integrity of windows equipped with vacuum glazing. The present contribution structures the different aspects that need to be considered in utilization of vacuum glazing in thermal retrofit, describes applied evaluation methods, first results of the ongoing research project, and illustrates the influence of various rebate depth and length of the edge seal on thermal transmission of the window.

Zespół SAPHO jako potencjalna przyczyna przewlekłego zapalenia kości żuchwy oraz zaburzeń funkcji stawów skroniowo-żuchwowych – opis przypadku

SAPHO syndrome (synovitis, acne, pustulosis, hyperostosis, osteitis) is a rare disease, with an unknown, probably multifactor etiology, comprising osteoarticular disorders of aseptic inflammatory character, and cutaneous changes of massive acne or palmoplantar pustulosis type. Usually the changes involve the anterior thoracic wall, and sternoclavicular and sacroiliac joints. According to literature reports, the mandible is affected in 10% of cases. The paper presents a case of SAPHO syndrome in an 18-year-old patient, with the involvement of the right body, angle, and branch of the mandible and the right temporomandibular joint. Considering the results of imaging examinations (computed tomography, magnetic resonance, and scintigraphy), as well as laboratory, histopathological and microbiological investigations, the authors discuss the possible diagnostic problems and the differentiation of SAPHO syndrome with other diseases. The article also presents different treatment methods, including temporomandibular joint reconstruction with the use of an alloplastic prosthesis. The aim of the paper is to present SAPHO syndrome as a potential cause of primarily chronic mandibular bone inflammation and stomatognathic system dysfunction.

Sound Transmission between Rooms with Curtain Wall Façades: A Case Study

Curtain walls have reached good performances in terms of façade sound and thermal insulation, as well as solar protection. Nevertheless, the sound insulation performance of the partition between adjoining rooms with continuous curtain wall façades is often reduced by the presence of direct and flanking transmission through the junction with the façade itself. In this work, flanking and direct structural transmissions are analysed with reference to the joints of the mullion of the curtain wall with lightweight plasterboard partitions. Airborne sound insulation and vibration measurements were made in two adjacent rooms affected by the acoustic problems determined by the curtain wall joint. Traditional acoustic measurements, carried out according to EN ISO 16283–1, highlighted problems in sound insulation between rooms, but without any indication on different sound transmission paths through the wall. Vibration measurements were made for every part of the system (frame columns and beams, window panes, plasterboard wall, plasterboard false ceiling, etc.) to better understand the sound transmission paths in these kinds of structures. In this paper the results of this analysis are presented. Moreover, taking into account previous works and measurements made in this research field, different solutions for curtain wall structures are analysed and technical suggestions are given to improve airborne sound insulation between rooms separated by partitions mounted up to metal frames.

Trass-lime reinforced mortars in strengthening and reconstruction of historical masonry walls

The paper describes the behaviour of tensile joints in irregular external faces of stone walls and the results of laboratory testing of selected technologies for strengthening mortar, which can be applied in strengthening, repair and renovation of historical stone masonry walls, with special references to structures with irregular faces. A research programme of the Building Institute at Wrocław Technical University on the effectiveness of strengthening irregular, three-leaf stone masonry walls using modern technologies is also presented.Special attention is devoted to technologies introducing stainless steel tie-rods Ø2mm in diameter into joints in the external wall face in conjunction with filling joints with trass-based mortar (TUBAG TWM). Results of laboratory testing of plates (40×160×138mm) of mortar reinforced with various types of synthetic fibres. Tests were carried out based on a four-point bending, which was treated as representative from the point of view the static behaviour of the reinforced tensile joints in the wall. The possibilities of curtailing the first cracking, strengthening and deflection of the trass-lime mortars are also described, in situations where the stress value exceeds that at which first cracks appear (FSD – first crack, strengthening, deflection). Composites were strengthened with dispersed polymer fibres, steel tie-rods, polypropylene and carbon netting. The analysis indicates that there is a need to identify a hybrid form of reinforcement as an effective solution for strengthening mortars in historical buildings, including joints in historical stone walls.

Determination of heat losses of a window frame to the wall joint when replacing the outdated constructions of window blocks with modern ones

In the Soviet Union a lot of residential buildings with wooden window systems were built. In the last 15 years the requirements to heat protection of buildings have strengthened and the technologies of window systems production have developed. New window constructions appeared, in which window frames of PVC profiles are used. So now double-casement windows with glass are replaced by single-casement with glass units. The replacement of windows is associated with a number of specific problems. The authors analyzed the quantitative parameters of the heat losses in the claddings of brick buildings. It was revealed that significant heat leakage occurs in the joint areas of window frame with the wall, at the junction of slopes. The authors offer a quantitative calculation of heat losses in these units in case of two-dimensional heat flux based on thermal conductivity matrix taking into account the convective heat transfer. On the basis of this calculation a computer program was developed that allows pinpointing the most problematic areas for choosing rational actions for elimination of cold bridges.

Quantitative estimation of joint roughness coefficient using statistical parameters

where τ is the peak shear strength of the rock joint, σ is the normal stress, JRC is the joint roughness coefficient, JCS is the strength of joint wall, φb is the basic friction angle. Over the last half century, researchers have kept working on techniques for estimating JRC of rock joints for or from this model. So far, the JRC value of a particular rock joint is most often estimated by visibly comparing it to the ten standard profiles with JRC values ranging from 0 to 20 [2]. This method was also adopted by the ISRM commission on test methods since 1981 [3]. In rock engineering practice, however, the visible comparison has been long thought to be subjective in that the user has to judge which profile his joint fits the best. The development of objective methods was gradually advanced by researchers considering quantitative estimation. Tse and Cruden [4] established regression correlations between JRC and Z2 (the root mean square of the first deviation of the profile) proposed by Myers [5] and SF (the structure function) by Sayles and Thomas [6]. As Tse and Cruden's equations have correlation coefficients as big as 0.986, they are often employed to estimate JRC [7,8], though Z2 and SF were later found by Yu and Vayssade [9] and Yang et al. [10] to be sensitive to the sampling interval. Yu and Vayssade [9] argued that Tse and Cruden's preparation of the discrete point data was improper, as an isotropic transformation (enlarging the standard profiles by 2.5 times both in xand y-coordinates) may exaggerate the roughness of the joint profiles. They manually digitized the ten standard profiles at three different sampling intervals of 0.25, 0.5 and 1.0 mm and indicated strong influences of sampling interval on JRC estimated by Tse and Cruden's equations. Yang et al. [10] reconstructed the ten standard profiles by means of Fourier transform and updated the correlations between JRC and Z2 as well as SF. Their equations display even higher correlation coefficients (0.99326) (Table 2). Besides Z2 and SF, Rp was also taken as one of the parameters to estimate JRC of a rock joint. Rp was firstly defined as roughness profile index by El-Soudani [14], which is equal to the ratio of the true length of a fracture surface trace to its projected length in the fracture plane. Maerz et al. [12] employed the ten standard profiles and related their JRCs to Rp, which gave a linear relationship with a correlation coefficient of 0.984. Yu and Vayssade [9] also proposed to estimate JRC using RL. Though RL was considered by Yu and Vayssade [9] as “real profile length”, the authors found it is identical to Rp according to its calculation provided in Yu and Vayssade's appendix. Wang [13] derived an empirical equation with R as the parameter to estimate JRC, where R was called as “elongation rate” and

Modelling of shear characteristics at the concrete–rock mass interface

An analysis of shear characteristics on the concrete–rock mass interface is presented, in order to simulate the effect of load at the contact of concrete structure of the dam and the rock foundation. The analysis is based on the real mechanism of shear, which is different from the so-called the “saw tooth” model that simulate the walls of joints in the rock mass. As a result, the analytic form of shear deformation and shear strength as a function of normal and shear loads, as well as the mechanical characteristics of the rock mass, is established. In this way, mathematical models are derived that can be used for structural analysis of Concrete Dams for the Preliminary Design level. The models are developed on the basis of a large number of shear tests carried out on the concrete blocks at the concrete dam sites, during the period from the seventies to the present day.

Effect of MIG Welding Method Choice on Hot Cracking Occurrence in EN AW 6082 Aluminium Alloys

The article presents the course and the results of research on welding conditions and tendency of hot cracking occurrence connected with MIG (CMT or Pulse) welding method choice. EN AW 6082 alloy is considered hard-to-weld by using conventional arc welding processes (MIG-Pulse) due to the heat sensitivity and the tendency to hot cracking in the thin walled joints (weld, HAZ). MIG low energy method (CMT) was developed inter alia to solve this problem.

Seismic response of precast, posttensioned concrete jointed wall systems designed for low- to midrise buildings using the direct displacement-based approach

Seismic response of precast, posttensioned concrete jointed wall systems designed for low- to midrise buildings using the direct displacement-based approach

ИСПЫТАНИЯ ПЛАТФОРМЕННЫХ СТЫКОВ НЕСУЩИХ КОНСТРУКЦИЙ КРУПНОПАНЕЛЬНОГО ЖИЛОГО ДОМА

The data on the results of tests of two series of platform joints in external and internal walls for a 14-storey panel house are given. The objective is determination of a breaking load. Constructions were simulated by concrete elements of actual thickness, 300 mm long and 400 mm wide. The nodes rigidity was ensured by special metal bonds. The strength of concrete and mortar was determined by a complex method: sample tests and nondestructive tests. The minimum breaking load for the joint of exterior walls was 64 ton. The strength margin taking into account the safety factoris 1.33. The minimum breaking load for the joint of interior walls was 103 ton. The strength margin is 1.17. When testing three products in each series the minimum breaking load was at least 90% of the reference load, specified on the basis of the safety factor 1.6. Keywords: structure test, platform joint, concrete strength, breaking load.

Analysis of large concrete storage tank under seismic response

This study adopted the finite element software ABAQUS to trace the dynamic response history of large reinforced concrete storage tank during different seismic excitations. The dynamic characteristics and failure modes of the tank’s structure were investigated by considering the rebar’s effect. Calculation results show that the large concrete storage tank remains in safe working conditions under a seismic acceleration of 55 cm/s2. The joint of the concrete wall and dome begins to crack when seismic acceleration reaches 250 cm/s2. As the earthquake continues, cracks spread until the top of the wall completely fails and stops working. The maximum displacement of the concrete tank and seismic acceleration are in proportion. Peak displacement and stress of the tank always appear behind the maximum acceleration.