Connection Details Research Articles

Cyclic behavior of dual-steel beam-to-column welded flange-bolted web connections

Cyclic loading tests on dual-steel beam-to-column welded flange-bolted web connections were conducted to quantify their moment resistance, plastic deformation and energy dissipation capacities. The test program consisted of five one-sided connection specimens, where Q355 grade beams and Q690 grade columns were used, to study the effects of beam-to-column welded flange connection details and panel zone shear strength on the connection seismic performance. Two types of welded connection details were considered; one was the traditional complete-joint-penetration (CJP) welded connections by use of backing bars, and the other type was those with the bottom backing bar further reinforced by a fillet weld. Three column web thicknesses were designed to arrive at strong, intermediate and weak panel zones, respectively. It was found that the CJP weld with the backing bar reinforced only under the bottom beam flange produced satisfactory performance and accommodated plastic rotations larger than 0.03 rad, while a maximum plastic rotation of 0.04 rad could be developed in the high-strength steel panel zone before fracture occurred. These results evidenced that those dual-steel connections could still sustain high seismic deformation demands.

Abnormality of the pulvinar in posterior cortical atrophy: A multimodal MRI study

AbstractBackgroundAlthough the pulvinar is known for its extensive connections with both ventral and dorsal visual streams, details of pulvinar functional connectivity in the setting of posterior cortical atrophy (PCA) remain unclearTo study pulvinar functional connectivity and relevant associations with higher visual dysfunction in PCA.MethodA total of 29 patients with PCA and 30 normal controls were recruited. Each participant underwent comprehensive neuropsychological assessment and both structural and resting‐state functional MRI scanning. Voxel‐based morphometry (VBM) and seed‐based functional connectivity analyses were conducted to assess pulvinar gray matter volume as well as connectivity between the pulvinar and whole brain regions. A partial correlation analysis was performed to analyze neuropsychological test and pulvinar imaging data.ResultCognitive and visual functions including visuospatial processing, visual perception, episodic memory, and naming were impaired among PCA patients. Marked pulvinar atrophy was noted in PCA patients. Furthermore, functional connectivity between the pulvinar and precuneus was significantly decreased in PCA patients as compared to normal controls (FWE corrected; P<0.001). Left pulvinar gray matter volume was found to associate with object agnosia (r = 0.42, P<0.05) and right–left disorientation (r = 0.29, P<0.05) among PCA patients. The bilateral pulvinar region was found to associate with Boston Naming Test (left, r = 0.51, P = 0.015; right, r = 0.46, P = 0.03) and Activities of Daily Living (left, r = ‐0.46, P = 0.019; right, r = ‐0.53, P = 0.006) scores. Correlation analyses did not reveal significant findings concerning functional connectivity.ConclusionOur findings confirm pulvinar degeneration and its contributions in the setting of PCA.

Experimental and analytical investigation on the progressive collapse resistance of precast concrete beam-column subassemblies with connecting steel bars

The resisting mechanism of precast concrete (PC) structures against progressive collapse varies from different types of beam-column connection details. In this context, the progressive collapse resistances and the corresponding resisting capacity models for the widely adopted PC structures with additional connecting rebars is significant when extreme events frequently occurred from time to time. In this study, progressive collapse resistance of one emulative PC beam-column subassembly and two PC specimens with connecting rebars were experimentally and analytically investigated. It is found that flexural action, compressive arch action (CAA) and tensile catenary action (TCA) were sequentially developed. Compared with the emulative specimen, the specimens with connecting rebars exhibited higher CAA and TCA capacities and dissimilar failure modes by dispersing the concentrated deformations at the beam ends to other locations. To elucidate such differences, a modified CAA model considering the real stress state of reinforcements and a TCA model accounting for the tensile steel force’s direction and the difference in failure mode were proposed. Experimental validation shows that the proposed models is effective to predict the CAA and TCA capacities with good accuracy. The findings in this study are beneficial to the understanding and formulation of the progressive collapse resistance of PC structures for practical engineering design.

Out-of-Plane behaviour of dowel type precast Panel-to-Foundation connections

Precast concrete wall panels are a common structural system, particularly in low-rise industrial and commercial buildings. In past earthquakes the connections between precast concrete panels and other structural members have been found to perform poorly. Fourteen panel-to-foundation assemblages were tested to investigate the out-of-plane performance of common connection detailing. These connection details included both dowel starter bars formed from conventional reinforcement, such as hooked bars, as well as starter bars connected to the panel via the use of cast-in threaded inserts. Variations in panel strength and connection strength were incorporated across the range of tested assemblages, and both cyclic and monotonic loading conditions were considered within the test program. It was found that conventional starter bars performed well because the presence of the hook returns of the starter bars within the joint region elevated the joint strength. Conversely it was found that panels having threaded inserts performed unsatisfactorily due to flexural cracking that propagated vertically behind the insert heads, leading to separation of the panel from the starter bars. It was determined that because the panels were close to the minimum reinforcement ratio, that the drift demands were very sensitive to the assumed cracking moment of the panel. Due to the brittle behaviour of the panel-to-foundation connection, it is advised that existing panels utilizing this connection be limited to less than 2% drift in the out-of-plane direction in order to avoid joint failure.

Efficient design of overlapped purlins loaded by gravity

Cold-formed steel represents a competitive solution for a wide range of structural applications due to its efficient use of material and its rapid manufacturing and installation. Concerning the purlin systems, continuous Z-shaped steel purlins overlapping over the intermediate rafters are the best choice to minimise material use. The connection between two purlin segments can be achieved by overlapping the profiles over the supports. Using a finite element model validated against experimental data, an extensive study was performed to identify the parameters that influence the design of overlapped purlins loaded by gravity. The analysis is performed on a two-span continuous beam under gravity loading. To capture as much as possible the real behaviour of the purlin, the sheeting is included in the model. The design of lapped purlins was found to be primarily influenced by the length of the span and the overlap length. The detail of the lapped connection is relevant only for short overlaps. A material efficiency study was performed to determine how the overlapped purlin should be designed to minimise material use. Numerical results demonstrate that short overlaps behave poorly from a material efficiency point of view. The optimal overlap length Lp1 + Lp2 was found to be between 15 and 25 % of the length of the span. Connection details or the use of unsymmetric overlaps do not bring a significant increase in terms of material efficiency. However, the use of higher-grade steels bring great improvements.

Experimental study on longitudinal shear behavior of prefabricated steel-concrete composite beams with notched connections

To address the fit-up issues caused by the interference between shear connectors and extended transverse bars, a novel deck-to-girder connection detail, notched connection, is applied to steel-concrete composite bridges with partial-depth deck panel (PDDP) systems. In the novel joint detail, protruding transverse reinforcement is replaced by evenly distributed notches at the ends of precast panels, and tie bars inserted in the notches are anticipated to resist longitudinal shear stress, achieving shear connection between steel girders and precast deck slabs. Considering the discontinuity of bottom transverse reinforcement, a four-point bending test was performed to investigate the longitudinal shear behavior of composite beams incorporating notched connections. Experimental findings indicate that the configuration of transverse reinforcement critically influences the failure modes of composite specimens, which involve crushing of concrete slabs, longitudinal shear cracking and splitting. Notably, tie bars sufficiently anchored in notches function equivalently to extended bars spliced by welding, and the specifically designed U-shaped notches enhance the anchorage performance of tie bars. Transverse reinforcing bars placed in the concrete topping prove more effective in resisting longitudinal shear than those in the bottom layer, and therefore asymmetrically reinforced concrete slabs experience reduced longitudinal shear cracking and splitting. Moreover, interface shear reinforcement effectively ensures the full composite action, while concentrated point loads can induce excessive local longitudinal shear stress. The study also provides design recommendations for notched connections.

Numerical investigation of a novel concrete-to-steel column splice in mixed structures in height

Buildings in which the type of structural material changes between their stories are referred to as mixed-in-height structures. Typically, these buildings have concrete structures in lower stories and steel structures in upper stories. Valuable investigations have been conducted on mixed-in-height structures to explore their seismic response and changes in structural natural period due to the sudden change in the lateral stiffness at transition level and mass irregularity, but scant attention has been given to the connection between steel and concrete structures at varying heights. Given the geometrical limitations of existing concrete structures, the dimensions of steel columns in supplementary stories must align with those of reinforced concrete columns. Consequently, building codes have not yet provided guidelines for proper connection details and effective load transfer from upper steel to lower concrete structures which is crucial due to the abrupt changes in stiffness and force transfer mechanisms in such splice connections. Thus, this study considers Numerical investigation on two full-scale laboratory tested specimens, with similar details but different axial loads, and numerical analysis of a new connection between a concrete and a steel column at the transition level. This research examines the aforementioned connection under two boundary conditions. Furthermore, after validating the numerical models with experimental specimens, axial load parameters, relative percentage of reinforcement to concrete area, and the force–displacement diagrams are presented. Finally, a numerical model of a three-story column in a frame is analyzed using finite element analysis under lateral load, and the sequence of plastic hinge formation is studied. The practicality and effectiveness of the proposed splice was verified herein. Furthermore, the average value of ductility (µ) was calculated to be 5.5, while exhibiting negligible overstrength factor (Ω). Similar response parameters were calculated for F-AL-R2 (43.2 kN/mm, 21.1 kN/mm) and F-AL-R3 (43.8 kN/mm, 22 kN/mm), indicating that the influence of increased rebar percentage diminishes at higher values. The analysis demonstrates that column connection failure did not occur, and the sequence of hinge formation was from top to bottom, validating the suitable performance of the proposed connection.

Study on fatigue performance of steel bridge welded joints considering initial defects

Orthotropic steel bridge decks (OSBDs) are extensively utilized in both medium-span and long-span bridges due to their lightweight and high strength properties. The current predominant method for connecting steel bridge decks is welding. However, the discontinuous geometric shape and inevitable welding defects at the welded joints are prone to stress concentration. This leads to fatigue cracks in steel bridge decks predominantly occuring at locations where defects are present within the welded joints. This study analyzes the fatigue performance and crack propagation of the rib-to-deck connection details considering the influence of initial defects. The experimental results of the T-joint revealed that the undercuts exerted a substantial influence on the fatigue performance, whereas partial penetration had a relatively small impact. The S–N curve of the specimen with undercuts can be derived by reducing 4 standard deviations from the S–N curve without initial defect. Alternatively, the fatigue strength of the specimen without initial defects can be divided by a safety factor of 1.4. The Paris formula was employed to compute pertinent parameters for crack propagation, followed by the utilization of the finite element method to simulate the process of crack propagation within the rib-to-deck details. The feasibility of this approach was confirmed by the simulation results. Furthermore, this study discussed the impact of initial crack size parameters on crack propagation mode and fatigue performance, providing valuable insights into the mechanisms underlying the fatigue crack propagation within welded joints of steel bridges.

Analytical investigations of seismic performance of different joint details for composite RCS frames

AbstractComposite RCS frames, comprising of Reinforced Concrete (RC) column and Steel (S) beam are gaining popularity as an attractive alternative to traditional steel moment frames for mid to high‐rise buildings as well as conventional RC construction for low‐rise buildings. The prime concerns with RCS frames are constructability and load transfer at beam‐column connections. Over the last 30 years, several joint details, viz. face bearing plates, erection steel columns, vertical joint reinforcement, and steel band plates have been proposed for RCS frames. The moment‐rotation behavior of these joints was established through quasi‐cyclic experimental programme. The moment‐rotation characteristics of RC column‐S steel beam joint significantly affect seismic performance of the overall frame. The objective of this paper is to evaluate the seismic performance of low and mid‐rise RCS moment resisting frames with different connection details, available in published literature. The nonlinear analyses of differently jointed RCS moment resisting frames is carried out and performance assessed in terms of collapse capacity and the available response reduction factor, Ravl. Seismic collapse risk of RCS frames is estimated to understand performance under uncertain ground motion.

Specific distortion‐induced fatigue failure at main girders of a railway bridge – efficiency of different reinforcements based on strain measurements

AbstractAt the main girders of a three span continuous girder railway bridge, built in the 1960s, through‐thickness cracks were detected in the web, at the location of the transverse stiffener to main girder connections. The transverse stiffeners are not welded to the girder flange, in order to increase their fatigue resistance. Instead, fitting strips between the stiffeners and the bottom flanges were used.First of all, the paper presents the results of local strain measurements at the original detail, without any reinforcement, for individual train passages. These results confirm a distortion‐induced fatigue failure, due to an unexpected high‐frequency oscillation of the web plate. Based on that, three different types of reinforcement were developed and installed at the bridge. For each type of reinforcement further strain measurements were done during regular train service. Also, a weigh‐in‐motion‐system was installed, to specify a representative passenger and freight train each. From the local strain measurements, during the passage of these two trains, the stress‐spectra were evaluated for all three types of reinforcement. Furthermore, existing fatigue test data of a similar connection detail from the literature were reassessed in order to provide an accurate fatigue resistance for the damage accumulation. The comparison of the evaluated fatigue damage of these individual stress spectra indicates the efficiency of each type of reinforcement.Finally, also representative reduction factors of the initial stress ranges without reinforcement, were developed for each type of reinforcement. This allows a more generalized assessment, regarding the efficiency of the different types of reinforcement, not just valid for individual trains but also for the whole train traffic.

Construction Technology of Steel Structure Prefabricated Panel Wall

Prefabricated steel structure buildings and prefabricated partition walls generally have many joints and pores. Therefore, prefabricated steel structure prefabricated panel walls and steel structures can achieve high air tightness requirements, which can be solved by deepening the connection between prefabricated panel walls and steel columns, steel beams, and gaps, and conducting air tightness treatment. Based on an example of a steel structure residential building project in Yinzhou District, Ningbo, this article focuses on introducing the connection details and gap treatment of prefabricated panel walls, steel columns, and steel beams, and analyzing key technical control points.

Seismic and collapse behavior of existing high-rise steel buildings under long-period earthquakes

This work presented the experimental and numerical evaluation of the seismic and collapse behavior of Japanese existing high-rise steel buildings subjected to long-period ground motions (LPGMs). Initially, the experiment (E-Defense, 2008) was performed by the full-scale shaking table tests on a typical 21-story steel frame substructure. Accordingly, a nonlinear rotational spring model was used in the numerical modeling. In consideration of the stiffness/strength deterioration and fatigue fracture of beam-column connections, the cyclic pushover analysis was utilized to account for such effect using seismic response data from system-level testing. Subsequently, the numerical model parameters were derived and validated with the initial experiment on the high-rise steel frame substructure. Herein, a well agreement on the seismic failure behavior between simulation and experiment was found in this situation. Furthermore, both field-welded and shop-welded connections on the seismic performance were included for comparison. For the 21-story prototype steel building (built before 1970s), a series of numerical collapse analyses were performed. The above revised model using nonlinear static pushover analysis and time history analysis were conducted to simulate and compare the effects of connection details and composite slabs on the 21-story prototype building. Finally, a cyclic loading protocol for simulating LPGMs was proposed, and the related ultimate failure behavior of the high-rise building was analytically discussed. Critically, this work should provide a viable strategy to numerically simulate the seismic and collapse behavior of high-rise steel buildings in this progressing construction field.

Distinct molecular profiles of skull bone marrow in health and neurological disorders

The bone marrow in the skull is important for shaping immune responses in the brain and meninges, but its molecular makeup among bones and relevance in human diseases remain unclear. Here, we show that the mouse skull has the most distinct transcriptomic profile compared with other bones in states of health and injury, characterized by a late-stage neutrophil phenotype. In humans, proteome analysis reveals that the skull marrow is the most distinct, with differentially expressed neutrophil-related pathways and a unique synaptic protein signature. 3D imaging demonstrates the structural and cellular details of human skull-meninges connections (SMCs) compared with veins. Last, using translocator protein positron emission tomography (TSPO-PET) imaging, we show that the skull bone marrow reflects inflammatory brain responses with a disease-specific spatial distribution in patients with various neurological disorders. The unique molecular profile and anatomical and functional connections of the skull show its potential as a site for diagnosing, monitoring, and treating brain diseases.

Full-scale testing and nonlinear finite element analysis of a pioneering fully prefabricated noise barrier wall system

The structural behavior of a novel fully prefabricated noise barrier wall system was examined experimentally and analytically using nonlinear finite element analysis. The wall components and connectivity details were developed to be a totally precast system for fast-track construction. Two full-scale prototypes were designed, fabricated, assembled, and prepared for full-scale testing at the High-Bay Structural Laboratory at the University of Illinois at Chicago. Each prototype was instrumented with about 40 sensors including strain gauges, linear variable differential transducers, and crack meters at pre-identified critical locations essential for understanding its structural behavior. In addition, a nonlinear finite element analysis model of the wall system prototype was required for future refinement and adjustment of the noise barrier wall system components. With proper calibration based on the experimental results, the nonlinear finite element analysis model will allow for conducting parametric studies on key factors relevant to the wall behavior without the need for costly and time-consuming full-scale testing. The structural behavior of the wall system was analyzed in terms of the load–deflection curves, load–strain curves, cracking, uplift, and failure mode. The experimental results revealed that the wall system was structurally stable up to a high loading level and met the intended serviceability and strength requirements.

Seismic performance of bolted T-stub Beam-to-Box column connection

Using internal continuity plates in box columns due to accessibility problems and complicated detailing of connection was perceived as fraught with shortcomings and limitations. To overcome this deficiency, the effectiveness of external continuity plates in conjugation with T-stub connectors in I-beam to box-column connections under cyclic action is investigated in this study. Three damage control strategies based on the fuse action of T-stubs (T-F), strengthening the connections (T-S), and using reduced beam section (RBS) connections (T-R) are pursued and are compared to a corresponding end-plate connection (E). Nonlinear finite element analyses are conducted using the ABAQUS/STANDARD software on the connections under the qualification cyclic loading conditions to elucidate all the main seismic behavioral aspects, including the strength, initial stiffness, energy dissipation, ductility, von-Mises stress, and equivalent plastic strain distributions of models. First, the accuracy of numerical models is validated by a series of available experimental results. Then, a parametric study is performed on the effects of the moment ratio of the beam to column, the number of continuity plates, stiffeners embedded on the beam, and using high strength materials on the seismic performance of the connections. From the results, it is found that the T-S model was the most efficient among the different connections studied, supplying the stiffness, strength, energy absorption, and ductility increases by 2%, 21%, −17%, and 22%, respectively with respect to the E model, satisfying the requirements of AISC Seismic Provisions for SMF. Increasing the beam-to-column moment ratio and the number of continuity plates, had limited effects by less than 10% on the seismic performance of the connections. In the absence of continuity plates, the connections exhibited worse inelastic seismic performance with decreases in stiffness, strength, and energy dissipation up to 67%, 44%, and 74%, respectively. The T-F connection gained a 13% strength increase and satisfied the AISC requirements when high-strength T-stubs are used. Based on the numerical observations, design strength and rotational stiffness of the proposed connections on the component-based joint design strategies, are finally outlined.

Seismic behaviour of assembled monolithic concrete coupling beams through tests of two-story coupled shear walls

In the prefabricated concrete shear wall structure, in order to further improve the construction efficiency, the underwindow wall and the wall pier on both sides are often prefabricated as a whole. Therefore, the assemble integral coupling beam is composed of a prefabricated under-window wall, a cast-in-place strip and a prefabricated upper-window wall. The failure mode of this type assemble integral coupling beam under cyclic loading has not been reported. Because the wall under the window is also merged into the coupling beam, the length-to-depth ratio of the coupling beam is further reduced. However, the upper and lower walls are prefabricated standard walls with opening, which cannot be configured with inclined bars, which is a common way for cast-in-place coupling beams with relatively small length-depth ratio. In addition, how to connect the upper and lower prefabricated walls is also a key problem that affects the seismic performance. Six, two-story, full-scale assembled monolithic coupled concrete shear walls were tested to investigate the seismic behaviour of the new assemble integral coupling beam and the role of coupling beam aspect ratio (1.5, 1.85, 2.4) and connecting method (with and without grouted sleeves) between prefabricated panels on seismic performance. Two specimens were tested for each beam aspect ratio, one with a single row of grouted sleeves in the under-window panel used to splice reinforcement between the two precast panels and the other without sleeves. Test results indicate that damage in specimens with beam aspect ratios of 1.5 and 1.85 resulted from flexural yielding of beam reinforcement followed by diagonal cracking of the coupling beams, whereas damage in the specimen with larger aspect ratio (2.4) was primarily due to flexural hinging at the ends of the coupling beams. The connection details greatly affect the type and degree of damage, and more concentrated damage was observed in specimens without grouted sleeves along the interface between the precast under-window panel and cast-in-place strip. However, whether the grouted sleeve connection was used had little effect on the load capacity, deformation and stiffness of the specimens. Drift ratios at 15% drop in the peak strength ranged from 1.1% to 1.6%. The flexural capacity of the assembled integral coupling beam can be calculated as one beam according to the formula of the conventionally CIP concrete coupling beam.

Evaluation of a modular construction system in accordance with the Passivhaus standard for components

Passivhaus is an energy performance standard for buildings that has been deeply analyzed in the current scientific literature. However, the study of the Passivhaus standard for components and the use of certified components in the construction of new nearly-zero energy buildings have not been thoroughly discussed. Additionally, hygrothermal performance evaluations of components in accordance with this standard have not been fully presented to the scientific community. This paper addresses this topic and aims to evaluate the hygrothermal performance of a Spanish modular construction system of extruded aluminum, in accordance with the criteria for Passivhaus components, suitable for warm temperate climate. A three-part methodology was implemented, including hygrothermal performance simulations on fourteen connection details comprising wall, roof, window, and floor solutions. The initial outcomes reveal that only four connection details fully meet the Passivhaus criteria for components. Therefore, an optimization of the connection details is proposed to validate the Passivhaus suitability of the construction system. The connection details are redesigned to reduce thermal energy losses in the junctions and to eliminate the risk of interstitial condensation. Several simulation processes are then conducted and the new results are compared against the criteria for components, validating the Passivhaus suitability. The evaluation presented in this paper provided valuable data that enabled to later optimize and submit the construction system to the Passivhaus Institut to become the first lightweight metallic construction system for walls and roofs manufactured in Spain with a Passivhaus certification for warm temperate climate.

Design code review on seismic demand and base detailing criteria: an application to wine tanks in Marlborough

Marlborough is the largest wine-growing region in New Zealand. The seismic events of Lake Grassmere 2013 and Kaikōura 2016 caused severe business disruption to the wineries due to the poor performance of wine storage tanks and connected non-structural components. The damage recorded raised two main discussions concerning the NZSEE 2009 guidelines for seismic design of liquid storage tanks. The first is related to the appropriateness of the determination of the importance level to adopt for the design of tanks. In fact, importance level 1 (IL1) (structures presenting a low degree of hazard to life and other property) was adopted for most wine tanks, and therefore, the horizontal forces designed were extremely low. Adopting importance level 2 (IL2) (normal structures) would have increased the overall seismic demand to design them for and therefore limited their structural damage but potentially increased the structural cost. The second concerns the design detailing of the critical connections. In fact, the current guidelines/standards lack provisions. The authors compare the NZSEE 2009 guideline with Eurocode 8 (EC8) and API 650 through the design of six tanks with typical dimensions used in the New Zealand wine industry. Results show that assigning importance level 1 results in seismic design demand similar to EC8 and API 650, thereby showing that other countries have a similar approach to New Zealand. A further comparative analysis also highlighted that connection detailing design including the hierarchy of strength is totally missing in all three standards/guidelines, which lacks information.

Performing Fatigue State Characterization in Railway Steel Bridges Using Digital Twin Models

Railway infrastructures play a pivotal role in developing the national transportation system. Recently, the strategy of the railway engineer has been significantly shifted; along with the development of new assets, they tend to pay increasing attention to the operation and management of existing railway assets. In this regard, this paper proposes a Digital Twin (DT) model to improve fatigue assessment efficiency in the operational processes of railway steel bridges (RSBs). The DT concept mainly lies in the federation and interaction of a Fatigue Analysis System (FAS), which is based on Eurocodes principles, and a model in Building Information Modeling (BIM). Along with the proposed DT concept, a prototyping system for a real bridge is initiated and curated. The FAS is validated in good-agreement results with the ambient vibration test of the bridge (about 1.6% variation between numerical and experimental values), and close values were found between numerical and experimental stresses, the latter obtained by installing strain gauges on the bridge. The BIM model provides access to the numerical values of fatigue state results in a given bridge connection detail but also automatically represents that information in a 3D environment using a color-scale-based visualization process. Furthermore, a simulation model with the main input variables being the traffic and geometric conditions of the bridge is continuously updated for timely re-evaluation of the damage state, which shows promise for the lifecycle management of the bridge.

Seismic Performance of Precast Shear Wall Systems and Connection Details for Underground Structures

Seismic Performance of Precast Shear Wall Systems and Connection Details for Underground Structures