Joint Details Research Articles

Seismic performance of eccentrically braced frames

The main objective of this research is to assess the seismic performance of Eccentrically Braced Frames of different configurations. Modelled Eccentrically Braced Frames subjected to both linear and nonlinear analysis in SAP 2000. The linear analysis gives an insight to mode shapes and mass participation ratios. The nonlinear analysis includes the pushover analysis, which provides information about the collapse mechanisms and performance points. This study also extended to compare the performance of Eccentrically braced frames with the performance of Special Moment Resisting Frames that helps to understand the structural efficiency of both systems. This study concludes that all selected configurations of Eccentrically braced frames undergo small roof displacement that is well below the target drift whereas SMRF frames will show large displacement. 2D braced EBFs shows a better post yielding behaviour and is more ductile compared to other frame systems. Shear links in the EBF frames increase the stiffness of the frame which in turn results in high base shear demand. Post yielding behaviour of EBF frames can be improved by proper detailing of beam-column joints and link connections which confirms that performance of EBF frames is superior to SMRF frames in seismic areas.

Fatigue life analysis of supercharged boiler based on the design by analysis method

Supercharged boilers are widely used as the core equipment of ship steam-power plants. A 1:1 model is built considering the connection details of tube-tubesheet joints. Furthermore, numerical simulation of stress field and fatigue life based on the DBA method is conducted. The results show that the maximum equivalent stress amplitude of 253.81 MPa appears on the tube-tubesheet joint of the tube plant radiation area. The total stress amplitude is dominated by the thermal stress range. The last calculated permissible number of cycles based on the fourth strength theory is 161,744 times, which is 15.7% higher than the result calculated by the third strength theory.

Submodelling method for modelling and simulation of high-density electronic assemblies

In order to enable the computation of fatigue life prediction of high-density electronic assemblies (solder joints > 4000), a modified submodelling approach was developed to integrate the detailed interconnections into equivalent layers with consistent mechanical parameters and thus reduce the complexity of modeling and simulation. The approach incorporates the uniform equivalent interconnect layers into the global model and simulate the general system response to thermo-mechanical loads. Displacements calculated from this first simulation are fed into a local model with more details of worst-case solder joints, in order to obtain local indicator of fatigue life. In this paper, referred to mechanical experimental methodology, a FEA process was used to extract the mechanical parameters of the equivalent layer. The validity of the modified submodelling approach was verified on fatigue life prediction of a high-density flip-chip package under thermal cycling.

A Method of DC Arc Detection in All-Electric Aircraft

Arc faults in an aircraft’s power distribution system (PDS) often leads to cable and equipment damage, which seriously threatens the personal safety of the passengers and pilots. An accurate and real-time arc fault detection method is needed for the Solid-State Power Controller (SSPC), which is a key protection equipment in a PDS. In this paper, a new arc detection method is proposed based on the improved LeNet5 Convolutional Neural Network (CNN) model after a Time–Frequency Analysis (TFA) of the DC currents was obtained, which makes the arc detection more real-time. The CNN is proposed to detect the DC arc fault for its advantage in recognizing more time–frequency joint details in the signals; the new structure also combines the adaptive and multidimensional advantages of the TFA and image intelligent recognition. It is confirmed by experimental data that the combined TFA–CNN can distinguish arc faults accurately when the whole training database has been repeatedly trained 3 to 5 times. For the TFA, two kinds of methods were compared, the Short-Time Fourier Transform (STFT) and Discrete Wavelet Transform (DWT). The results show that DWT is more suitable for DC arc fault detection. The experimental results demonstrated the effectiveness of the proposed method.

Investigation of Cracks Observed on a Skewed Bridge Constructed Using Self-Propelled Modular Transporters

This study investigates full-depth deck cracks observed on a skewed bridge, which was constructed using self-propelled modular transporters (SPMTs). To investigate the causes, three main factors associated with structural design, material design, and construction are reviewed. Specifically, the bridge performance under thermal and construction loading is investigated by conducting a nonlinear finite-element analysis. The analysis parameters include bridge deck geometry, boundary conditions, bearing details, and skew angles. The loading conditions mainly include thermal and differential deck movements induced during an SPMT move. The results are compared to a crack map created from two site visits. It is concluded that skewed decks are more susceptible to cracking than straight decks due to an asymmetric expansion and contraction. Additionally, semi-integral abutment designs in a skewed bridge increase the extent of cracking in the skewed corners of the abutment ends. It is recommended that a semi-integral abutment design be carefully considered when designing a skewed bridge and that bearing and expansion joint details need careful attention for accelerated bridge construction.

The Design of a Real-Scale Steel Moment-Resisting Frame for Pseudo-Dynamic Earthquake Testing

Background: Forthe reliable prediction of the non-linear response of structures, severe seismic events have proven to be a challenging task. Although much non-linear analysis software exists, the accuracy of the results depends on the assumptions made in the characterization of the members. Typically, the analytical models are calibrated using experimental observations. With this scope, experimental research remains the most reliable mean for the assessment of the seismic performance of structures, and it is crucial to target the development of new analytical models and design methods. Objective: Quasi-static tests can provide information on the non-linear behaviour of subassemblies, but it is often difficult to relate the imposed force or displacement histories to those that might occur during an earthquake. The pseudo-dynamic method combines an on-line computer simulation with experimental information about the tested structure, providing the application of realistic dynamic response histories. In this paper, the preliminary analysis and the design of a pseudo-dynamic testing facility for the experimental study of a real scale two storeys-two bays steel MRF, with classical and innovative joint details, are shown. Methods: Pushover and Incremental Dynamic Analyses carried out with Seismostruct software estimate the forces and displacements expected at each storey for the selected ground motions. These analyses have been performed by varying the structural detail of the beam-to-column connections. Results / Conclusion: In this paper, the analytical prediction of the performance of two bays-two storeys steel frames equipped with different solutions of beam-to-column joints is focused. Based on the performed analyses, it has been recognized that steel frames with partial strength joints can provide satisfactory performance under severe seismic actions provided that the joints are adequately designed.

JointSearch: Efficient parametric detailing preparation through user-defined and property-based joint type filtering

Detailing joints are important when designing structures. In this design process, a structure is divided into different joint types. Digital fabrication and algorithmic aided design have changed the conceptions and requirements of joint detailing. However, parametric tools that can efficiently identify joint types based on the solution space are not available. This article presents a methodology that efficiently generates topological relations and enables the user to assign joint instances to joint types. A series of property-based search criteria components is applied to define the solution space of a joint type. Valid joints are coherently filtered, deconstructed and outputted for detailing. The article explains both the methodology and programming-related aspects of the joint type filtering. The article concludes that the developed methodology offers the desired flexibility and may be suitable for other materials and applications.

Axial Compressive Behaviour of Square through-Beam Joints between CFST Columns and RC Beams with Multi-Layers of Steel Meshes.

The axial compressive behaviour of an innovative type of square concrete filled steel tube (CFST) column to reinforced concrete (RC) beam joint was experimentally investigated in this paper. The innovative joint was designed such that (i) the steel tubes of the CFST columns were completely interrupted in the joint region, (ii) the longitudinal reinforcements from the RC beams could easily pass through the joint area and (iii) a reinforcement cage, including a series of reinforcement meshes and radial stirrups, was arranged in the joint area to strengthen the mechanical performance of the joint. A two-stage experimental study was conducted to investigate the behaviour of the innovative joint under axial compression loads, where the first stage of the tests included three full-scale innovative joint specimens subjected to axial compression to assess the feasibility of the joint detailing and propose measures to further improve its axial compressive behaviour, and the second stage of the tests involved 14 innovative joint specimens with the improved detailing to study the effect of the geometric size of the joint, concrete strength and volume ratio of the steel meshes on the bearing strengths of the joints. It was generally found from the experiments that (i) the innovative joint is capable of achieving the design criterion of the ‘strong joint-weak member’ with appropriate designs, and (ii) by decreasing the height factor and increasing the volume ratio of the steel meshes, the axial compressive strengths of the joints significantly increased, while the increase of the length factor is advantageous but limited to the resistances of the joint specimens. Because of the lack of existing design methods for the innovative joints, new design expressions were proposed to calculate the axial compression resistances of the innovative joints subjected to bearing loads, with the local compression effect, the confinement effect provided by the multi-layers of steel meshes and the height effect of concrete considered. It was found that the proposed design methods were capable of providing accurate and safe resistance predictions for the innovative joints.

Investigation of U-bar joints between precast bridge decks loaded in combined bending and shear

This study proposes two types of U-bar joints: rectangular joints with stainless steel ties and T-shaped joints. The mechanical properties of four joint specimens subjected to combined bending and shear forces were studied experimentally and numerically. The T-shaped joint details effectively increased the cracking load and controlled the development of interface cracks. The bearing capacity of the four joint details were similar. Furthermore, a formula to estimate the bearing capacities of the T-shaped U-bar lap joint specimen is proposed, and its accuracy is verified.

Extremely-Low-Cycle Fatigue Damage for Beam-to-Column Welded Joints Using Structural Details.

The multiaxial fatigue critical plane method can be used to evaluate the extremely-low-cycle fatigue (ELCF) damage of beam-to-column welded joints in steel frameworks subjected to strong seismic activity. In this paper, fatigue damage models using structural detail parameters are studied. Firstly, the fatigue properties obtained from experiments are adopted to assess ELCF life for steel frameworks. In these experiments, two types of welded specimens, namely, plate butt weld (PB) and cruciform load-carrying groove weld (CLG), are designed according to the structural details of steel beam and box column joints, in which both structural details and welded factors are taken into account. Secondly, experiments are performed on three full-scale steel welded beam-to-column joints to determine the contribution of stress and/or strain to damage parameters. Finally, we introduce a modification of the most popular fatigue damage model of Fatemi and Socie (FS), modified by us in a previous study, for damage evaluation, and compare this with Shang and Wang (SW) in order to examine the applicability of the fatigue properties of PB and CLG. This study shows that the modified FS model using the fatigue properties of CLG can predict the crack initiation life and evaluate the damage of beam-to-column welded joints, and can be subsequently used for further investigation of the damage evolution law.

Cyclic loading tests of thin-walled square steel tube beam-column joint with different joint details

To study the seismic performance of a thin-walled square steel tube beam-column joint of a light steel frame, 8 kinds of thin-walled square-hollow structural steel (HSS) and concrete-filled steel tube (CFST) beam-column joints with different joint details were designed and manufactured. The joint details were divided mainly into welded joint, plate joint, angle joint and angle with stiffener joint. A total of 14 specimens of beam-column joint specimens were tested using a low reversed cyclic loading test. The failure characteristic, load-bearing capacity, hysteretic property, stiffness degradation and energy dissipation were compared. The results showed that the different joint details had a great influence on the seismic performance of the beam-column joint. The bearing capacity and failure rotation of the welded joint were poor. The bearing capacity of the plate joint was close to that of the welded joint, but it showed improved bearing capacity, failure rotation and energy dissipation capacity of the joint. The bearing capacity of the angle joint was poor. With the angle welded stiffener, the bearing capacity, stiffness and energy dissipation capacity of the joints were significantly improved. The number and height of the stiffener can improve the seismic performance of the joint. The stiffness and energy dissipation capacity of the CFST beam-column joint was better than that of the HSS beam-column joint with the same joint detail. The classification of the joint is discussed, and a simplified M-R calculation model is proposed.

Advanced joint slip model for single-angle bolted connections considering various effects

Latticed structures are commonly used in transmission towers due to lightweight, fast fabrication, and easy installation, but they generally experience more complicated structural behaviors. The full-scale tests on transmission towers have revealed large discrepancies between the numerical simulation and experimental results because the significant joint slip effects have not well considered in the former. The existing joint slip models were so simple that many key parameters had not been taken into account. Thus, a comprehensive joint slip model is proposed in this article for better prediction and design of tower structures. First, a full-detailed finite element model based on ABAQUS incorporating more realistic parameters for a typical joint is developed and calibrated by the experimental data from the literature. Furthermore, the proposed FE model is used for parametric study of joint behaviors with considerations of bolt pretension, friction at contact face, angle sizes and plate thickness, steel and bolt grades, number of bolts, and hole tolerance. Finally, an advanced joint slip model is provided for further incorporation in the second-order direct analysis of transmission towers. This work is limited in the literature and will significantly improve safety and enhance the cost-efficiency of tower design. The proposed model shows high accuracy and can be simply determined by joint details in line with the component method specified in Eurocode 3-1-8.

Service Life Design of Deck Closure Joints in ABC Bridges: Guidelines and Practical Implementation

Closure joints are commonly used in bridge deck to connect two adjacent prefabricated elements in accelerated bridge construction. The current practice of closure joints utilizes the use of different materials such as normal strength concrete and ultra-high performance concrete with the use of different reinforcement details such as straight bars, hooked bars, and headed bars. The design of closure joint to meet strength limit state is quite simple, however, the design for service life for these joints is quite challenging. Framework for service life design of closure joints in bridges, built using accelerated bridge construction techniques, is developed in this paper. This framework includes several steps: 1) identification of project requirements especially those influences the service life of closure joints; 2) identification and selection of feasible closure joint types suitable for the project requirements; 3) identification of factors which influence the service life of closure joints along with mode of failures and consequences; 4) identification of suitable approaches or strategies for mitigating failure modes or assessing the risk of damage; 5) modification of closure joint detail using mitigation strategies which may result in the development of several alternatives and options for each closure joint type; 6) estimation and comparison of service life for each modified alternative using finite or target service life approach; and 7) conducting life-cycle cost analysis for each modified alternative along with the selection of the optimum closure joint details to meet both strength and service life demand. This framework is used in practical design implementation example for 1400-ft long bridge in Boston, Massachusetts, US. Several closure joints details were studied under this research such as the use of normal strength concrete with straight bars, 180-degree hooked bars, 90-degree hooked bars, and headed bars along with the use of ultra-high performance concrete with straight bars. This paper summarizes the outcome of the design for service life of those closure joints comparatively.

TIME REDUCTION EFFECTS OF STEEL CONNECTED PRECAST CONCRETE COMPONENTS FOR HEAVILY LOADED LONG-SPAN BUILDINGS

The characteristics of large logistics buildings are their long spans and the ability to take heavy loads. Usually, PC components are used for their frames to ensure quick construction. However, the erection of most pin jointed PC structures increases the time and the cost incurred for ensuring structural stability and construction safety. To solve this problem, “smart” frames have been developed, which have tapered steel joints at both ends of the PC components. A smart frame with the moment frame concept not only assures structural stability and construction safety, but it also simplifies and quickens the erection because of its tapered joint detail. The purpose of this study is to compare the erection time and cost effects of the steel connected PC components for heavily loaded long-span logistics buildings with the existing PC frames. For this study, we selected a logistics building constructed with PC components and redesigned it as the smart frame, and the erection simulations were performed. We analyzed the time reduction effects of the smart frame. Our results confirmed that the use of the smart frame reduced the erection time and cost practically. Our investigations will help develop the erection simulation algorithms for smart frames.

Optimization and prefabrication of timber Voronoi shells

We introduce a variant of the timber grid shell, the timber Voronoi shell, whose surface is reticulated by Voronoi tessellation and whose edges are made of discrete dimensional timber. This work explores form-finding methods of the Voronoi shell as a compressive funicular shell. Two closed-form solutions to shape initialization are proposed. We develop methods for minimizing the deviation from coplanarity between timber members and adjacent surface normal in order to facilitate manufacturing. A well-defined fabrication process is important for making the physical structure consistent with the structural model. A 6-axis robot with a motor spindle is employed to prefabricate the timber so the in situ manual assembly becomes easier. A parametric model describes the joint details. We formulate the robotic toolpath as a closed-form function of the resultant mesh from form finding. Thus, a general-purpose programming language can directly implement the mesh optimization and manufacturing processes without CAD or CAM software. The physical implementations, including an exhibition pavilion, validated the approach.

Austempered ductile iron-to-steel dissimilar arc-welded joints: fatigue strength assessment according to local approaches

The design of mechanical components increasingly requires the adoption of different materials in the same structure with the aim of improving its performance. One of the available solutions is to adopt dissimilar arc-welded joints, which typically must withstand high fatigue loadings during in-service life. In a recent paper, the fatigue strength of EN-JS-1050 austempered ductile iron-to-S355J2 steel dissimilar arc-welded joints was experimentally investigated by testing some typical welded details in the as-welded conditions, under either axial or four-point bending loadings. In the present work, previous experimental campaign has been extended by fatigue testing other ADI-to-steel joint details. The fracture surfaces of all tested joints have been analysed to identify the fatigue crack initiation locations. Then, experimental fatigue results have been re-analysed to determine the fatigue strength category of each welded detail, which have been compared with those provided by International Standards for corresponding homogeneous steel joints. Afterwards, the local approach based on the Peak Stress Method (PSM) combined with the averaged Strain Energy Density (SED) fatigue criterion, has been used for the first time for fatigue strength assessment of ADI-to-steel dissimilar arc-welded joints. First, the structural volume size R0 has been calibrated for joints exhibiting fatigue crack initiation and propagation at the ADI side; then, a PSM-based fatigue design curve has been determined by fitting the available experimental results.

PHOTOGRAMMETRY AS A TOOL FOR LIVING ARCHITECTURE

Abstract. Living Root Bridges (LRBs), grown by rural Khasi and Jaintia communities in Meghalaya (India), are the best known example of functional living architecture. Over 70 bridges, as well as ladders, pathways and platforms have been grown from a single species (Ficus elastica), using a collection of construction methods in regionally specific environmental conditions. In general, living architecture exhibits geometric complexity for which documentation and representation tools are yet to be established. Photogrammetric surveys provide data-rich point clouds which could be useful for analysis and design specific to living architecture. This study provides the first photogrammetric surveys of LRBs. Useful point clouds were produced for several bridges, as well as joint details. The method is found to have a range of benefits: providing detailed views, showing environmental conditions, and allowing for time analyses. The wider application of photogrammetry to living architecture is discussed, particularly with regards to Baubotanik structures and the improved documentation and representation of LRBs as a unique architectural typology. The need for developing a tool for topological model extraction, and possible methods therein is discussed.

Reduction in Shear Lag Effects in Tall Buildings Using Exterior Bracing and Diagrid Systems (Recent Developments-review paper)

The structural and architectural aspects of the exterior bracing and diagrid systems - two systems which generally reduce building materials, enhance structural performance, and decrease overall construction cost achieve sustainability. When a structure is completed it is expected to look elegant, appealing and, above all it must be structurally correct. These structural systems, diagrids and exterior bracings can visually communicate the inherent structural logic of a building while giving artistic effect. This creates the structural elements that are aesthetically pleasing and geometrically coherent, while also respecting the laws of mechanics. The diagrid (diagonal grid) structural system has now become increasingly popular. A diagrid system consists of series of triangles and horizontal rings of beams which provide the structure support against gravity and lateral forces, while also making a building stiffer and often lighter than a traditional high-rise. Diagrids are usually composed of steel, because of its high strength and ability to resist both tensile and compressive forces. The diagrid can suffer from problems of implementation due to its complicated steel joints, but recent advances in joint detailing and prefabrication are helping to address this issue. Due to their triangular configuration, diagrids can efficiently carry the shear and moment caused by lateral loads and gravity. They are effective in minimizing shear deformation, providing maximum resistance against torsion. In this paper, shear lag effect is being studied based on various works reported and is correlated with stiffness of the building. The study is also done for the different patterns of bracing systems the blend of structural performance and aesthetics, examined to facilitate a better understanding of the aesthetic developments in skyscrapers around the world. For this purpose, different geometric patterns of bracing system are considered. For a relative study for shear lag effect, cross-sectional dimensions of beam and columns, their alignments (column) and the material properties are assumed to be same throughout the height of the building. It is found that bracing system considerably reduces the shear lag effect and hence increases the building stiffness to withstand lateral loads.

Experimental seismic behavior of squat shear walls with precast concrete hollow moulds

This study proposes an innovative precast shear wall system, called an EVE precast hollow shear wall structure (EVE-PHSW). Precast panels in EVE-PHSW are simultaneously precast with vertical and horizontal holes. Noncontact lap splices of rebars are used in vertical joints connecting adjacent precast panels for automated prefabrication and easy in situ erection. The seismic behavior of EVE walls was examined through a series of tests on six wall specimens with aspect ratios of 1.0∼1.3. Test results showed that EVE wall specimens with inside cast-in situ concrete achieved the desired “strong bending and weak shear” and failed in shear mode. Common main diagonal cracks and brittle shear failure in squat cast-in situ walls were prevented. Inside cast-in situ concrete could significantly improve the shear strength and stiffness of EVE walls. The details of boundary elements (cast-in situ or prefabricated) and vertical joints (contiguous or spaced) had little effect on the global behavior of EVE walls. Noncontact lap splices in vertical joints could enable EVE walls to exhibit stable load-carrying capacity through extensive deformations. Evaluation on design codes revealed that both JGJ 3-2010 and ACI 318-14 provide conservative estimation of shear strength of EVE walls, and EVE walls achieved shear strength reserves comparative to cast-in situ walls. The recommended effective stiffness for cast-in situ walls in ASCE 41–17 appeared to be appropriate for EVE walls.

Seismic response of precast and IBS buildings under earthquake attacks

Poor performances of precast buildings during earthquakes were due to inadequate connections between the structures components, insufficient seating and anchorage and poor workmanship and quality materials used. It is important to investigate their seismic performance by conducting experimental work, analyzing the data and modelling them using nonlinear time history analysis of the earthquakes. Three types’ structural components of precast structures and Industrialized Building System (IBS) were designed, constructed, tested, analyzed and modelling in this chapter. There structural components are precast shear-key wall panel, beam-column joints and tunnel form building system. All these specimens were tested under in-plane lateral cyclic loading. The seismic performance parameters such as lateral strength capacity, stiffness, ductility and equivalent viscous damping were evaluated using the measured hysteresis loops from experimental work. The findings from this research work can be implemented and enforced by government and local authorities to pay special attention to joint detailing of precast structures components while constructing the precast buildings. The design concepts and detailing of the jointing precast structural components contribute significantly to the overall seismic performance of precast buildings under earthquakes excitations. A lot of structural damages occurred during earthquakes due to not using the current seismic code of practice and poor detailing especially at the jointing system.