Diaphragm Plates Research Articles

Mechanical behavior improving study of concrete deck of main beam at pylon root of composite beam cable-stayed bridge

Steel-concrete composite beam has been increasingly applied to large span cable-stayed bridges. It takes full advantage of the material properties of steel and concrete. However, the concrete deck bears tension in the negative moment zone, such as zero block, which is disadvantageous to structures. Aiming at this problem, a finite element model of the zero block in the negative moment zone of a semi-floating cable-stayed bridge is built, and the local mechanical performance of the bridge deck under completed status is studied. Based on the analysis results, three improvement measures have been proposed. The improvement effect of each method and composed of three methods has been studied. The numerical results show that the whole zero block zone is in the compressed state under the combined action of the bending moment and axial force of the stay cable. However, the local negative moment effect in the zero block zone is very prominent under the support of the diaphragm plate. Removing parts of the diaphragm plate at the bearing position can significantly improve local mechanical behavior in the concrete deck, which transfers the local support to the adjacent two diaphragm plates. The composed improvement effect is prominent when the three measures are adopted simultaneously.

Seismic performance of special-shaped hexagonal concrete filled steel tubes with inner diaphragm plates and shear studs

With the development of the high-rise buildings, the columns with special cross-sectional shapes are frequently adopted for architectural and aesthetic purposes. The concrete filled steel tube (CFST) is a reasonable choice for such requirement due to the characteristics of excellent seismic performances, construction efficiency and strong adaptability to special shapes. This paper focuses on the seismic performance of a special-shaped hexagonal CFST column with an inner diaphragm plate and shear studs adopted in a super high-rise building. Experiments were conducted on five column specimens under axial compressive force and lateral cyclic loading to investigate the influence of various parameters including loading angle, axial compression ratio, shear studs and the type of in-filled concrete. In one of the specimens, the ultra-high performance concrete (UHPC) was used as the in-filled concrete to substitute the conventional normal strength concrete, and the effects on the capacity and ductility of the column were revealed. Then the failure mode, the load-deflection curves, seismic performance indexes and the strain distribution were analyzed. The flexural capacities of the columns were evaluated by the fiber section model, where the failure criterion considering the buckling of steel tube was proposed and the effects of studs were included. Finally, the contribution to axial force and bending moment from outer steel tubes, inner diaphragm plate and in-filled concrete were calculated and compared based on the proposed model. It is found that the fiber section model considering the steel plate buckling and strengthening effects of studs precisely predicted the moment-curvature curves and the flexural capacity of the test specimens. The contribution of the inner diaphragm plate was considerable which could not be neglected.

An Evaluation of the Tribological Characteristics of Diaphragm Plates for High-Pressure Hydrogen Gas Compressor Applications

Diaphragm plates, a key part of high-pressure hydrogen gas compressors, are easily cracked or broken due to repeated shape deformations caused by pressure, resulting in increasing difficulties in maintenance. This study aimed to improve the durability of diaphragm plates. This investigation focuses on the potential for friction and wear reduction through the application of surface polishing and Teflon coating on two diaphragm plate materials, namely stainless steel 301 and Inconel 718. To achieve this, various metal substrates with diverse surface morphologies were prepared and subjected to comprehensive assessments of their surface, mechanical, and tribological properties. Research findings revealed that the surface hardness and tensile strength of stainless steel 301 surpassed those of Inconel 718. Through friction and wear analysis, it was observed that Teflon-coated diaphragm plate material with a microstructure demonstrated superior friction performance. Furthermore, finite element analysis was employed to investigate the stress behavior of stainless steel 301 under different applied loads and conditions, offering valuable insights into the diaphragm’s performance. From the results of this study, the excellence of the Teflon coating applied to the surface of stainless steel 301—the material of the hydrogen compressor diaphragm plate—was confirmed.

Electroslag Welding Applications for Steel Building Construction in Japan: A State-of-the-Art Review

Electroslag welding (ESW) is advantageous for the improvement of the efficiency of welding thick steel plates, and the application of ESW has been gradually spreading to civil structures such as steel bridges and steel building structures. This paper presents a review of state-of-the-art ESW application for steel building structures in Japan. A brief history of the development of ESW technology, which involves the installation of interior diaphragm plates in welded built-up box columns for high-rise steel buildings, is first introduced, followed by a recent recommendation for the design and fabrication of ESW joints to prevent brittle fracture under earthquake loading.

Cyclic test and finite element analysis of a steel double K-braced frame with laterally-restrained plates for RC building retrofit

Damage was discovered in existing 24-story reinforced concrete (RC) buildings in New Taipei City under the 2015 Hualien earthquake with a magnitude of 6.3. A new scheme was proposed to retrofit the buildings by adding a steel concentrically double K-braced frame in a limited space, with diaphragm plates to laterally restrain each brace to increase its buckling strength. A cyclic test was first conducted on a full-scale steel braced frame specimen, composed of a steel boundary frame, two pairs of K-type-arranged plates for axially loaded braces, diaphragm plates for brace buckling restraint, and surrounding RC members. Secondly, a finite element (FE) analysis was conducted on the specimen for a correlation study and investigation of force transfer between the infilled braced frame and surrounding RC members. A finite element parametric study was then conducted on single braces with different numbers of restraint and plate thicknesses to investigate the cyclic behavior and buckling force. The AISC 360-16 (2016) provides a very conservative prediction of the brace bucking force, but the prediction based on Wolchuk (1963) reasonably matches well the test and FE analysis results. A cyclic backbone curve for a single brace modeling, considering in-plane lateral supports, was proposed in this work.

Experimental and numerical investigation of I-beam to concrete-filled tube (CFT) column moment connections with pipe-stiffened internal diaphragm

This paper presents an experimental and numerical investigation of two full-scale I-beam to concrete-filled tube (CFT) column internal-diaphragm moment connection specimens. In this type of connection, to allow the passage of concrete through the column tube wall, the internal diaphragms are perforated, which, as a result of drilling, creates stress concentration in these plates, reducing their strength and stiffness. In this study, first, to improve the diaphragms' performance, these plates were stiffened utilizing steel pipes, and the effect of this stiffening on the connection behavior under cyclic loading was investigated in the laboratory. In the second part, the specimens were analyzed by the finite element (FE) method in the Abaqus software. Results indicated that stiffening the internal diaphragm plates with the pipes increased the connection's flexural strength and cumulative energy dissipation by 20% and 22%, respectively. It also prevented the yielding of the diaphragm plates and increased the connection's stiffness by 8% to 22%. Furthermore, the stiffening of the internal diaphragms led to better stress distribution at the plastic hinge region in the beam and shifting of the maximum rupture index location from the outer edge of the beam flanges by about 40% of the beam flange width towards the beam's longitudinal axis. It was also concluded that the proposed connection with stiffened internal diaphragm meets the criteria for utilization in intermediate moment frames (IMFs) in seismic regions.

Seismic behaviour of novel self-tightening one-side bolted joints of prefabricated steel structures

In response to the requirements of building industrialization and sustainable development, prefabricated steel structures are vigorously promoted in recent years. The joint is an important part of prefabricated steel structures. The response of the structures under earthquake is directly determined by the seismic behaviour of the joints. Square steel tube columns and H-section steel beams are widely used in prefabricated steel structures due to the superior mechanical properties. Nevertheless, the bolted joints need to be operated on both sides. To solve this problem, a novel self-tightening one-side bolt (STOSB) was proposed based on the self-tightening high strength one-side bolt (SHSOB) developed by our research group. The behaviour and failure mechanism of the prefabricated steel structure joints based on the STOSBs under the low cyclic loading were revealed. Based on the existing experimental research, the finite element software ABAQUS was used to establish the refined numerical models of three fabricated steel joints. The numerical simulation analysis was carried out to verify the practicability of the STOSBs in practical engineering. The equivalent viscous damping ratio ζ - inter-story drift angle θ curve, hysteretic curve and skeleton curve of each specimen were obtained. On this basis, a parametric analysis was carried out to explore the effects of the column flange thickness, column diaphragm plates, endplate thickness, endplate stiffeners and other factors on the seismic behaviour of this novel joint. Subsequently, according to the moment - rotation hysteretic curves determined by the finite element analysis, a restoring force model of this novel joint under the low cyclic loading was established. The results show that the STOSBs can be used in practical engineering. The failure mode of each specimen is that a plastic hinge appears in the steel beam above the stiffeners. The endplate is always close to the column flange during the test. The seismic behaviour of the joint is significantly influenced by the endplate stiffness and column flange thickness. The bearing capacity, energy dissipation and rotational stiffness of the joint are enhanced with the endplate stiffness and column flange thickness increasing. Setting diaphragm plates in the steel column opposite to the upper and lower flanges of the steel beam can achieve similar results. When the stiffness of the endplate or column flange is weak, the moment - rotation hysteretic curve is full and the joint is a semi-rigid joint. When the stiffness of the endplate and column flange is strong, the moment - rotation hysteretic curve is in an elastic range and the joint is a rigid joint. The hysteretic behaviour of such joints under the low cyclic loading can be well simulated by the restoring force model established herein.

Calculation Method and Influence Factor Analysis for the Normal Working Life of Reinforced Concrete Highway Bridges

Aimed at the working life of bridges under the reiteration function of vehicle load, which is not mentioned in the current bridge design codes, this paper introduced the concept of normal working life. The authors regarded reinforced concrete bridges as the research object and proposed a fast method to calculate the working life to judge whether the working life can fit the requirement of design working life. On the basis of the equivalent constant amplitude stress amplitude method of Miner's criterion, the cumulative damages of the bridges were calculated, the average annual damage degrees were obtained by determining the relationship between cumulative damages and times, and the working life of the bridges was estimated. This method was applied to the calculations of T-beam bridges, and the influences of spans, transverse diaphragms, reinforcement ratios, vehicle loads, and S-N curve equations were analyzed. The calculation results showed that vehicle loads and S-N curve equations determine the accuracy of working life. The calculated life in accordance with the fatigue vehicle model in the specification is much longer than the design life. The load varies greatly from region to region. Compared with Guizhou Province, Jiangsu and Liaoning provinces have a higher traffic flow of heavy vehicles over 35 t, which results in years unfilled with the design life. With the increase in spans, the working life increases accordingly because the reinforcement ratios increase with the spans. The diaphragm plates and reinforcement ratios have a great influence on the working life. The working life of bridges with diaphragm plates is 18%-63% lower than that of bridges without diaphragm plates. The reinforcement ratios are lower, and the reduction rates of the working life are greater.

Seismic fracture evaluation of diaphragm joints in welded beam‐to‐box column moment connections

SummarySteel box columns are widely used in steel building structures in Taiwan due to their dual strong axes. To transfer the beam‐end moment to the column, diaphragm plates of the same thickness and elevations as the beam flanges are usually welded inside the box column. The electro‐slag welding (ESW) process is widely used to connect the diaphragms to the column flanges in Taiwan because of its convenience and efficiency. However, ESW may increase the hardness of the welds and heat‐affected zones (HAZs), while reducing the Charpy‐V notch strength in the HAZ. This situation can cause premature fracture of the diaphragm‐to‐column flange welds before a large plastic rotation is developed in the beam‐to‐box column joints. To quantify the critical eccentricity and the effectiveness of fracture prediction, this study uses fracture prediction models and finite element model (FEM) analysis to correlate the test results. In this study, two beam‐to‐box column connection subassembly tests are conducted with different loading protocols and ESW chamber shapes. To implement a fracture prediction model, the material parameters are established from circumferential notched tensile tests and FEM analysis. Test results indicate that the fracture instances can be predicted on the basis of the cumulative plastic deformation in the HAZs. Analytical results indicate that fracture instances and locations are sensitive to the relative locations of the ESW joints and beam flange. Tests also confirm that the possible fracture of the diaphragm‐to‐column flange joints can be mitigated by enlarging the chamber of the ESW joint.

On the distortion and warping of cantilever beams with hollow section

This paper deals with the stress analysis of a cantilever box beam subjected to static or fluctuating torsional moment loading. Such beams may have multiple critical locations from the strength point of view; one interesting detail is the cross section where the loading is imposed. However, such details can be typically designed to possess smooth shapes, resulting in moderate stress concentrations, which mean that fatigue failures can be avoided. However, the distortional deformation of the cross section induces transverse bending stresses, which may be detrimental, particularly in welded box beams. In addition, the fixing location where the beam is typically welded to an end plate may become a critical point. This paper presents an analytical approach for calculating the longitudinal stresses due to the warping of the cross section as well as the distortion-induced transverse and longitudinal stresses in rectangular hollow sections. Finite element analyses (FEAs) are carried out to verify the analytical approach to shed light on the critical points in the end plate details with different degrees of weld penetration using the effective notch stress (ENS) concept and to suggest design proposals for an efficient structural detailing of diaphragm plates to decrease the warping behavior.

Seismic Performance Evaluation of Steel Box-Column Connections with ESW Stiffeners

The purpose of this study is to evaluate the seismic performance of steel box-column connections with electro-slag welding (ESW) stiffeners. Steel box columns have been widely adopted in seismically active areas, such as Japan and Taiwan. It is a common practice to weld diaphragm plates to the inner walls of steel box columns using the ESW process. However, there is still a lack of study evaluating the seismic performance of these steel box-column connections. In the first part of this paper, a literature review examines ESW stiffeners and their impacts on steel box-column connections. In the second part, finite element analysis is conducted on ESW misalignment and eccentricity. The result shows a correlation between connection failures and ESW stiffeners. In addition, ESW fusion diameters can affect the connections more significantly than ESW eccentricities and the thickness of diaphragm plates.

FE modelling of replaceable I-beam-to-CHS column joints under cyclic loads

This paper presents a finite element investigation on the structural behavior of replaceable I-beam-to-CHS column joints with external diaphragm plates under cyclic loads. The finite element methodology was validated against complementary experimental results and satisfactory comparisons were observed between numerical and experimental results on the hysteretic curves, initial stiffness, bearing capacity, and energy dissipation. While validating the numerical models, two key parameters — preloading force and bolt hole sizes were identified which have significant effects on the structural performance. Based on the numerical and experimental results, recommendations on the design procedures were proposed.

Dynamic characteristic analysis and fatigue life estimation of steel-structure bridges under vehicle loading

Influenced by repeated effects of vehicle loads during an operation period, a bridge structure will suffer from cyclic stress, while the corresponding fatigue damage will be generated. Therefore, it is very important to conduct on fatigue performance analysis and life assessment of a bridge during the operation period. Firstly, vehicle load spectrums and dynamic stress are determined through using field vehicle recorder and strain gauge to measure stress responses of steel-structure bridge diaphragm plates. Results show that: No.1 strain gauge was closer to the hole edge than No. 2 strain gauge, and its stress concentration was more obvious; sequence of stress values is as follows: No. 1 strain gauge > No. 2 strain gauge > No. 3 strain gauge. Then, the vehicle load spectrums are loaded into the finite element model of the steel-structure bridge (with and without struts), so stresses at holes, weld and plates are computed. Stresses at holes and plates have the similar variation tendency, but stresses at the hole are larger. Variation of stresses at welds is more complicated than other two positions when vehicles pass by. Equivalent stress amplitudes at holes, plates and other positions in the steel-structure bridge (with struts) model are less than computational results of the steel-structure bridge (without struts) model, but stress amplitudes at the weld don’t vary obviously, indicating that force at holes and plates can be effectively improved by strengthening rigidity of the diaphragm plate using struts. Finally, fatigue lives of detailed parts for the steel-structure bridge are computed. Results show that applying struts can effectively increase fatigue lives of some detailed positions, which can further improve fatigue life of the whole steel-structure bridge.

Cyclic behaviour of external diaphragm joint to CHS column with built‐in replaceable links

AbstractA series of full‐scale laboratory experiments was conducted to investigate the cyclic behaviour of an external diaphragm joint between a steel I‐beam and a circular hollow section column. The joint incorporated two diaphragm plates (DPs) welded to the column's external wall and bolted to the flanges of the beam using tapered cover plates (TCPs). The joint was designed to limit yielding and plastic hinging of the TCPs while the other joint components remained elastic. This is necessary if the joint is to qualify for use in structures classified in the damage control structural performance range according to FEMA 356. Two parameters of the TCPs are investigated in this paper: steel grade and bolt preload force. The use of higher steel grades was found to impose undesirable higher strain demands on the beam and DPs and dissipate less energy than the joints with the lower grade. A controlled reduction in the bolt preload force allowed connection slippage to occur beyond the serviceability limit, created an additional energy dissipation fuse and allowed rotation of the plastic hinge region to exceed the 25 mrad required for medium ductility class structures.

Finite Element Analysis for the Mega Columns for XRL West Kowloon Terminus

Using ANSYS parametric design language, a three-dimensional finite element model is developed to analyze the stress distribution and the strength of the mega columns for XRL West Kowloon Terminus. The detailed von Mises stress distribution in each column, vertical stiffener plates and the diaphragm plates is obtained. From the analysis, the phenomenon of stress concentration is obvious in both upper and lower diaphragm plates. The local value of von Mises stress in them is higher than the yield stress value, which must be avoided by more detailed local structural design.

Detailing of I-beam-to-CHS column joints with external diaphragm plates for seismic actions

In this paper monotonic and cyclic finite element (FE) analyses are presented for the development of an I-beam-to-CHS column steel moment joint for seismic actions. The development process for the final joint details includes: (1) eliminating two identified structural deficiencies of distortion in column web panel and strain concentrations in the external diaphragms; (2) creating a multi-fuse energy dissipation mechanism; (3) devising a joint to delay onset of beam yielding. Two external diaphragm collar plates are welded to the circumference of the CHS column for connection to beam flanges. Various collar ring widths are examined for these horizontal diaphragms and a width (based on achieving full strength of the beam flanges) is found to produce an acceptable web panel performance. Different types of stiffener geometries in the connection region are then trialed to eliminate strain concentrations in the diaphragms. Two pairs of triangular diaphragm stiffeners are found to provide the desired performance. In order to produce a multi-fuse energy dissipation mechanism, tapered cover plates (TCPs) equipped with vertical stiffeners (VSs) are integrated into the joint. Oversized web holes of 4–10mm are required to enable inelastic deformation for an overall joint rotation of 60–100mrad, without undesirable web distortion. Further FE analyses are used to design the TCPs and VSs so they can be replaceable link post-seismic actions. For the final joint detailing it is shown that 6mm oversized holes for the TCPs will delay the occurrence of yielding in the beam until the joint rotation is 70mrad.

Stress Analysis of Transversely Loaded Functionally Graded Plates with a Higher Order Shear and Normal Deformation Theory

AbstractStatic analysis of orthotropic functionally graded (FG) elastic, rectangular, and simply supported (diaphragm) plates under transverse loads is presented based on a higher order shear and normal deformation theory (HOSNT). Although functionally graded materials (FGMs) are highly heterogeneous in nature, they are generally idealized as continua with mechanical properties changing smoothly with respect to the spatial coordinates. The material properties of FG plates are assumed here to be varying through the thickness of the plate in a continuous manner. The Poisson’s ratios of the FG plates are assumed to be constant, but their Young’s moduli vary continuously in the thickness direction according to the volume fraction of constituents, which are mathematically modeled as an exponential function. The governing equations of equilibrium for the FG plates are derived on the basis of a HOSNT assuming varying material properties. Numerical solutions are obtained by the use of the Navier solution method. ...

FREE VIBRATION OF FUNCTIONALLY GRADED PLATES WITH A HIGHER-ORDER SHEAR AND NORMAL DEFORMATION THEORY

Free vibration analysis of functionally graded elastic, rectangular, and simply supported (diaphragm) plates is presented based on a higher-order shear and normal deformation theory (HOSNT). Although functionally graded materials (FGMs) are highly heterogeneous in nature, they are generally idealized as continua with mechanical properties changing smoothly with respect to the spatial coordinates. The material properties of functionally graded (FG) plates are assumed here to be varying through the thickness of the plate in a continuous manner. The Poisson ratios of the FG plates are assumed to be constant, but their Young's modulii and densities vary continuously in the thickness direction according to the volume fraction of constituents which is mathematically modeled as a power law function. The equations of motion are derived using Hamilton's principle for the FG plates on the basis of a HOSNT assuming varying material properties. Numerical solutions are obtained by the use of Navier solution method. The accuracy of the numerical solutions is first established through comparison with the exact three-dimensional (3D) elasticity solutions and the present solutions are then compared with available solutions of other models.

Optimization of Sludge Dewatering Through Pretreatment, Equipment Selection, and Testing

Biological sludge dewatering is a crucial step in industrial wastewater treatment processes. There are always challenges as these sludges tend to form highly compressible cakes and the sludge properties are continually changing. In this work, a method was developed to optimize the selection and design of a dewatering process for these highly compressible materials and a case study was used to demonstrate this methodology. A Capillary Suction Time (CST) method was shown to be effective in the initial screening of pretreatment methods. Laboratory pressure filtration can show general trends of the dewatering behavior but cannot match plant-scale operation due to dissimilarities in the equipment configuration and operating procedures. A pilot filter press equipped with both chamber and diaphragm plates was found to work well for this evaluation. It was demonstrated that pressure filtration alone produces wetter cakes (30–34 wt% cake solids),but with the additional expression exerted by the diaphragm, drier (41–44 wt% cake solids) cakes can be produced. This work also shows that high sludge-handling capacity can be achieved by shorter cycle times, which can be advantageous, but is offset by the fact that this produces wetter cakes, increasing both the total amount of solids for final disposal and handling cost. The selection and design of a sludge dewatering process needs to include both cake dryness and sludge-handling capacity in the economics analyses to achieve the optimum design.

Higher order shear and normal deformation theory for natural frequency of functionally graded rectangular plates

A higher order shear and normal deformation theory (HOSNT) is presented for free vibration analysis of functionally graded (FG) elastic, rectangular, and simply supported (diaphragm) plates. Functionally graded materials (FGMs), although heterogeneous are idealized as continua with their mechanical properties changing smoothly with respect to the spatial coordinates. The material properties of FG plates are assumed to be varying through thickness of the plate in a continuous manner. Poisson's ratio is assumed to be constant, but their Young's moduli and densities vary continuously in the thickness direction according to the volume fraction of constituents, which is mathematically modelled as power law function. The equations of motion are obtained using Hamilton's principle employing HOSNT. Navier solution method is used to solve the equations of motion. The effect of variation of material properties in terms of gradation index on the natural frequencies of FG plates is studied in this article. In this study, the effects of aspect ratios, thickness ratio, material variations of FG plates on their natural frequencies are examined. It is thought that the tabulated results would be a reference for other researchers to compare their results.