Current Design Specifications Research Articles

Improved Methods for Simulating Live Loads for Two-Dimensional Structural Analysis of Buried Culverts

The current AASHTO LRFD Bridge Design Specifications stipulates a “special distribution width” for two-dimensional (2D) live-load analysis of reinforced concrete (r/c) boxes and arches with less than 2 ft of soil cover. This special distribution width allows a significantly greater reduction of the applied surface load than permitted for other culvert shapes and materials. Neither the AASHTO commentary nor the underlying developmental report provide the physical reasoning for the special distribution width, or why it only applies to r/c boxes and arches. This paper provides a clear, physical understanding of the three-dimensional (3D) phenomena associated with the special distribution width and the interaction with longitudinal load spreading through soil. This is achieved with the aid of a flat-plate model, representative of the top slab of a box culvert, with a variable line-load width. The closed-form solution reveals that the physical reason is “3D stiffness effects” (3DSE), which occur when the line-load width is relatively short compared with the culvert’s longitudinal lay length. Moreover, it is shown that 3DSE disappear when the line load reaches a special width called the “critical distribution width” or Wcritical. Wcritical is dependent on the culvert’s span and length, and is a key parameter along with parameter Wmin needed to identify the limiting line-load width that evokes 3DSE. The key concepts of 3DSE, Wcritical, and Wmin are used to develop improved 2D analysis procedures using either the traditional reduced surface load approach or the more recent continuous load spreading approach.

Strength Evaluation of a Bogie Frame by Different Methods

Some crucial loads that current strength design specifications have not taken into account are also considered when assessing the strength of a bogie frame. Calculation methods of these loads come from load analysis. Finite element simulation and fatigue test rig have been used to assess static strength and fatigue strength of a bogie frame. In addition to the two methods, actual running test is also used to assess bogie frame fatigue strength. In finite element simulation method, endurance limit and modified Goodman fatigue limit diagram are two important tools to judge whether fatigue strength of a bogie frame meets requirement. In actual running test method, Miner linear cumulative damage rule is used to assess bogie frame fatigue strength.

Behavior of shear connectors joined by direct fastening

Direct fastening is an effective method to quickly and easily connect two steel components. However, the behaviors of this kind of connection have been rarely studied and there is no direct reference to them in current design specifications. Therefore, it is now timely to investigate the properties and behavior of this type of connection. In this paper, 11 coupons were tested at room temperature and 24 coupons were tested at high temperatures and after fire, to examine the deterioration of the mechanical properties of the steel. Moreover, 24 samples that were connected by direct fastening were tested at high temperatures and post fire conditions to study the deterioration in the shear strength of the fastener at different temperatures. Furthermore, 100 samples that were connected by direct fastening were tested in an ambient temperature to examine the effect of the number of fasteners, fastener spacing, fastener arrangement, knurled fasteners and protuberance. Based on the tested results, a modified expression for the yield strength of this kind of connection was proposed. Besides that, the bearing resistance versus displacement (BRVD) of the connections was numerically modeled and plotted into a simple curve based on the three key parameters of yield strength, effectiveness stiffness and ultimate displacement.

Structural Design of Cold-formed Steel face-to-face Connected Built-up beams using Direct Strength Method

The structural behavior of cold-formed steel (CFS) built-up beams that are gaining interest in the construction industry is investigated in this study. As per the current American Iron and Steel Institute's (AISI) CFS structural members specifications (direct strength method), there are no explicit guidelines or procedures for the types of built-up sections being evaluated in this research. The present study, therefore, examines the suitability of using the current AISI design specifications for the design of CFS built-up beams. The built-up beams investigated in this study are assembled using two identical sigma sections, and interconnected face-to-face by discrete spot welding. The test parameters studied include the length of the member (L) and spacing (sl) between the interconnecting spot welds. Based on the failure modes observed in experiments, new limitations for the interconnection spacing (smax) of the face-to-face connected built-up beams that failed in distortional buckling is suggested. The design strength prediction (MDSM) for the tested built-up beams is calculated using current AISI design procedure for the purpose of verification and to extend the current design procedure for the built-up beams. The comparison between experimental tests and design predictions (MEXP vs. MDSM) indicates that the design results are unconservative and unreliable due to the incorrect failure mode prediction and overestimation of the critical elastic buckling stresses in the elastic buckling analysis which is a key input to the direct strength method of design calculations. Hence, modified design procedures and design equations were suggested for the CFS built-up beams after carrying out a comprehensive investigation on failure modes and numerical study that are vulnerable to fail in distortional buckling. It was also shown that the newly suggested procedures and equations are reliable for the design of CFS built-up beams.

Study on improvement of design method for airport flexible pavement in Vietnam

Presently, there are 22 airports in operation comprising of 9 international airports and 13 domestic airports in Vietnam. According to the master plan of airports national wide, there are 124 airports and aerodromes both civil airports and military airfield. Design of airport flexible pavement is an important step during design the airport runway and taxi. Currently airport flexible pavement in Vietnam designs based on Vietnamese national standards, American standards and Russian standards. However, these standards have some issues such as design load, effect depth of the aircraft load, relative deflection caused by the aircraft and critical relative deflection. Therefore, this research points out improper issues that is not compatible with current practices of increase in airplane total weight. It also clarifies unfavorable effects of existing flexible pavement design method to the performance of runway pavement in some airports in Vietnam. Some technical measures are proposed for improvement of the current flexible pavement design standards and specifications are also recommended.

VERIFICATION OF SIGNAL POLE SHAFT FOUNDATION LRFD DESIGN USING FINITE ELEMENT METHOD

This study presents verification methods of current shaft foundation design under linear lateral and torsional loads. Shaft is used as a foundation to support mast arm signal pole structure and transfer loads from superstructures to ground. The capacity of current shaft foundation deployed in the State of Maryland is re-verified due to higher sub-structural strength requirement against super-structural fatigue proposed from the AASHTO LRFD Specification (2015). The shaft foundation verification includes embedment length and torsional capacity. For embedment length check, lateral reactions between soil and shaft are verified by comparing analytical method and finite element method. Wind-induced torque is a design concern for the shaft of a single pole cantilever structure. However, torsional capacity of the shaft foundation of signal pole structures is rarely mentioned in the current design specification. By verifying finite element models with analytical method, torsional effect is further simulated to finite element models to evaluate the adequacy of current shaft foundation design. Results show existing design of shaft foundation could meet requirements to resist lateral force under extreme conditions. For torsional effect, current torsional capacity is less than the torque induced by wind load in the worst soil conditions.

Steel Design by Advanced Analysis: Material Modeling and Strain Limits

Abstract Structural analysis of steel frames is typically performed using beam elements. Since these elements are unable to explicitly capture the local buckling behavior of steel cross-sections, traditional steel design specifications use the concept of cross-section classification to determine the extent to which the strength and deformation capacity of a cross-section are affected by local buckling. The use of plastic design methods are restricted to Class 1 cross-sections, which possess sufficient rotation capacity for plastic hinges to develop and a collapse mechanism to form. Local buckling prevents the development of plastic hinges with such rotation capacity for cross-sections of higher classes and, unless computationally demanding shell elements are used, elastic analysis is required. However, this article demonstrates that local buckling can be mimicked effectively in beam elements by incorporating the continuous strength method (CSM) strain limits into the analysis. Furthermore, by performing an advanced analysis that accounts for both geometric and material nonlinearities, no additional design checks are required. The positive influence of the strain hardening observed in stocky cross-sections can also be harnessed, provided a suitably accurate stress–strain relationship is adopted; a quad-linear material model for hot-rolled steels is described for this purpose. The CSM strain limits allow cross-sections of all slenderness to be analyzed in a consistent advanced analysis framework and to benefit from the appropriate level of load redistribution. The proposed approach is applied herein to individual members, continuous beams, and frames, and is shown to bring significant benefits in terms of accuracy and consistency over current steel design specifications.

Estimation of response of skewed bridges considering pounding and supporting soil

Skewed bridges are prone to large in-plane rotations of the girders, especially when seismically-induced pounding with the abutments occur. These rotations have been associated with increase in relative displacements, leading to potential unseating or permanent dislocation of the girders, especially in the transverse direction. The approach adopted in current design specifications for the seat lengths of skewed bridges is oversimplified and could potentially underestimate the relative displacements. Shake table tests were performed on a 1:20 scale bridge-abutment model with 0° (straight), 30°, and 45° skew angles. The effects of pounding, supporting soil, and ground motions simulated based on different soil conditions were considered. The bridge segment and abutments experienced spatially uniform excitations. The results were used to develop empirical formulae for estimation of the relative displacements of skewed bridges. Normalisation of the responses means that the proposed approach can be incorporated into design specifications – as an amplification or reduction compared to that calculated for a straight bridge. It was found that the empirical formulae proposed in this study are able to provide more conservative estimates of the expected relative displacements of the girders of skewed bridges.

Formulae for Calculating Elastic Local Buckling Stresses of Full Structural Cross-sections

Formulae for determining the full cross-section elastic local buckling stress of structural steel profiles under a comprehensive range of loading conditions, accounting for the interaction between the individual plate elements, are presented. Element interaction, characterised by the development of rotational restraint along the longitudinal edges of adjoined plates, is shown to occur in cross-sections comprising individual plates with different local buckling stresses, but also in cross-sections where the isolated plates have the same local buckling stress but different local buckling half-wavelengths. The developed expressions account for element interaction through an interaction coefficient ζ that ranges between 0 and 1 and are bound by the theoretical limits of the local buckling stress of the isolated critical plates with simply-supported and fixed boundary conditions along the adjoined edges. A range of standard European and American hot-rolled structural steel profiles, including I-sections, square and rectangular hollow sections, channel sections, tee sections and angle sections, as well as additional welded profiles, are considered. The analytical formulae are calibrated against results derived numerically using the finite strip method. For the range of analysed sections, the elastic local buckling stress is typically predicted to within 5% of the numerical value, whereas when element interaction is ignored and the plates are considered in isolation with simply-supported boundary conditions along the adjoined edges, as is customary in current structural design specifications, the local buckling stress of common structural profiles may be under-estimated by as much as 50%. The derived formulae may be adopted as a convenient alternative to numerical methods in advanced structural design calculations (e.g. using the direct strength method or continuous strength method) and although the focus of the study is on structural steel sections, the functions are also applicable to cross-sections of other isotropic materials.

Slip Coefficient and Ultimate Strength of High-Strength Bolted Friction Joints with Compact Bolt Spacing and Edge Distance

In current design codes, the minimum bolt spacing and edge distance for high-strength bolted friction joints are specified based on the bolt diameter, regardless of the plate thickness or steel strength. However, the mechanical performance of joints with a more compact bolt spacing than that given in the current design specifications has been little examined. In this study, the slip and ultimate strength of high-strength bolted joints with a compact bolt spacing and edge distance were investigated. Tensile tests were conducted on friction-type joints with various bolt arrangements. The use of a compact bolt arrangement was not observed to have a negative influence on the slip strength in these tests. The estimated strengths corresponding to the experimentally observed failure modes were found to agree fairly well with the experimental results within a 10% error. A parametric finite element analysis was also conducted to investigate the influence of the bolt arrangement on the slip coefficient. It was concluded that the bolt spacing and edge distance have little influence on the slip coefficient.

Local buckling behavior of welded π-shaped compression stub columns

The local buckling behaviors of welded π-shaped stub columns were investigated experimentally and numerically in this study. Nine welded π-shaped columns made from Q345 steel with different width-to-thickness ratios were tested under axial compression. The material properties, initial geometric imperfections and welding residual stress distribution of specimens were measured. Results from the tests, including the strengths, the load-deformation responses, and the failure modes were presented. The strengths determined by tests were compared with the design strengths predicted by the current steel design specifications. The experimental studies were complemented by the numerical investigations, in which the finite element models were initially verified against the test results and subsequently used for parametric studies covering a wide range of cross-sections. The modifications on the Bleich formulas were derived to calculate the buckling coefficient of π-shaped section. Based on the experimental and parametric analyses, formula for direct strength method (DSM) was proposed to predict the compressive strengths of welded π-shaped stub columns, which offered reasonable predictions.

Sloped RBS Moment Connections at Roof Floor Subjected to Cyclic Loading: Analytical Investigation

Reduced beam section (RBS) steel moment connections are the prequalified connections in current design specifications and widely used in the US. Although RBS connection details are for general applications, they are not applicable for sloped beams at roof floors because the prequalified connections were developed based on the orthogonal beam–column conditions in a typical floor. A series of finite element analysis were conducted to investigate the effect of beam slope at roof floor on RBS connections. The results demonstrated that the connections at roof floor were vulnerable to fracture at the heel location when the beam was sloped down from the connections. But the stresses at the heel location were relatively small when the beam was sloping up. The downward beams developed plastic hinges accompanied by buckling, but the upward beams experienced only minor damage. Analysis results also indicated that the beam slope should not be more than 10° to adopt the prequalified connection details. The deformation at the heel location could be limited by introducing a rib plate at the connection and accordingly, the force demand at the connection could be effectively reduced.

Influence of multi-component ground motions on seismic responses of long-span transmission tower-line system: An experimental study

Seismic performance is particularly important for life-line structures, especially for long-span transmission tower line system subjected to multi-component ground motions. However, the influence of multi-component seismic loads and the coupling effect between supporting towers and transmission lines are not taken into consideration in the current seismic design specifications. In this research, shake table tests are conducted to investigate the performance of long-span transmission towerline system under multi-component seismic excitations. For reproducing the genuine structural responses, the reduced-scale experimental model of the prototype is designed and constructed based on the Buckingham\'s theorem. And three commonly used seismic records are selected as the input ground motions according to the site soil condition of supporting towers. In order to compare the experimental results, the dynamic responses of transmission tower-line system subjected to single-component and two-component ground motions are also studied using shake table tests. Furthermore, an empirical model is proposed to evaluate the acceleration and member stress responses of transmission tower-line system subjected to multi-component ground motions. The results demonstrate that the ground motions with multi-components can amplify the dynamic response of transmission tower-line system, and transmission lines have a significant influence on the structural response and should not be neglected in seismic analysis. The experimental results can provide a reference for the seismic design and analysis of long-span transmission tower-line system subjected to multi-component ground motions.

Influence of mechanical and geometric uncertainty on rack connection structural response

Steel storage pallet racks are used worldwide for storage of palletized goods and are popular for their ease of construction, customization, and economy. Failure of these racks can result in significant property loss and economic disruption. Ultimately, the structural behaviour of these systems can be characterized as braced systems, in the cross-aisle direction, and un-braced moment resisting frame systems, in down-aisle direction. The structural capacity of these moment resisting frames depends on the performance of beam-to-column connections. Rack connections are typically formed by beams welded to connectors with tabs and columns with perforated cross-sections to accept these tabs joining beams and columns without bolts. This paper aims to evaluate the influence on the structural response of rack connection due to the structural details, and randomness in the geometrical features and mechanical properties of connection members (beam, weld, connector and column). To explore the impact of variability in design parameters on the initial flexural stiffness and ultimate flexural capacity of rack connections, a Monte Carlo simulation was conducted, using the Component Method to model the connection. Variability in member geometrical features was determined from current design specifications, while variability in steel mechanical properties was determined via experimental tests. The results indicate that system effects reduce flexural stiffness and the variability in the response of individual components does not propagate to the overall flexural capacity. Ultimately, the work motivates accurate and thorough reporting of geometric and structural uncertainty to accurately assess rack connection performance.

SRASA: a Generalized Theoretical Framework for Security and Reliability Analysis in Computing Systems

Although there is a pressing need for highly secure and reliable computing systems, there is a glaring lack of formalism under which the properties of reliability and security can be jointly designed into these systems. This gap can primarily be attributed to the evolution of the two subfields. In the work, we introduce a unified generalized theoretical framework, called security and reliability aware state automaton (SRASA), to formally describe the specifications of a computer system that cover both security and reliability. SRASA is a 22-tuple finite state machine model that encompasses both physical and abstract states of the system, which may suffer from passive and active attacks. Three case studies illustrate the interpretation and application of the proposed SRASA theoretical framework. Our analysis and experimental results show that a non-physical attack may exploit unspecified or untested states to implement the malicious purpose, rather than introducing a new state to the system. To the best of our knowledge, this is the first attempt to bridge the current design specification gap between secure and reliable computing systems using a unified automaton approach. A general yet complete methodology that will encompass all aspects of system design, from the functional level specification to the gate level design at any system granularity, may not be feasible or it may be beyond the scope of a single work. Therefore, we aim in this work to (1) give an overview of the current landscape of reliability and security in systems design, (2) introduce a generalized framework to specify and reason about both reliability and security in the system design process, and finally (3) be general enough in the framework specification that it can be adopted or customized to more specific or concrete design instances.

Validation of a general design procedure for the transverse impact capacity of steel columns

There has been considerable interest over the past decade in the transverse impact response of steel columns and composite steel-concrete columns. While several researchers have developed analytical procedures for specific types of steel sections, a unified design approach has yet to be established. The present paper develops a generalised rigid-plastic procedure to calculate the design transverse impact capacity for a wide range of steel and composite column sections. The design procedure is specifically developed to align with current international hot-rolled steel design specifications, including those in Australia, North America, the European Union and China. A database of 320 impact experiments is collated from the literature, and used to validate the general design procedure. It is demonstrated that the procedure provides robust transverse impact capacity predictions for solid rectangular steel sections, steel I-sections, circular and rectangular steel hollow sections, concrete filled circular and rectangular steel hollow sections and concrete filled double skin steel hollow sections. In some cases stainless steel members were additionally included.

Shearing Bearing Capacity of Screwed Connections of Thin Steel Sheets

This paper reviews the design rules of single shear screwed connection of cold-formed steel structure in the current design specifications, such as North American, Australian/New Zealand, European, British, Japanese and Chinese, and points the shortcomings of Chinese design specification and the mistakes of some published reports on the shear resistance of single shear screwed connections. A total of 194 single screw overlap sheared connections, which were made of steel sheet manufactured in China and were tested by Chinese scholars since 1993, and the detailed test data are introduced. Using the design specifications mentioned above recalculated the normal connection shear strength of the 194 connection specimens, and evaluated the accuracy of six design specifications under the different failure modes. The Japanese design manual is too conservative to estimate the bearing capacity of the single shear screwed connection under any failure mode. For tilting or tilting and bearing failure mode, the accuracy of the AISI S100 and AS/NZS 4600 diminishes and sometimes tends to be unsafe; however, the Eurocode 3, BS5950-5 and GB50018 are appropriate. As to screw shear failure mode, the AISI S100, AS/NZS 4600, Eurocode 3 and BS5950-5 are appropriate but GB50018 tends to be unsafe. The paper gives a new design formula as a supplement to GB50018 that can accurately predict the bearing capacity of single shear screwed connection in all failure modes. Finally, the Group Effect of multiple-screw shear connection was investigated based on 38 multiple-screw connection specimens.

Effect of Binder Modification and Recycled Asphalt Pavement on the Performance of Permeable Friction Course

Permeable Friction Course (PFC) is a hot-mix asphalt that contains interconnecting voids that provide improved pavement surface drainage during rainfall. The objective of this study was to determine if PFC mixtures which incorporate reclaimed asphalt pavement (RAP) will provide performances that are similar to PFC mixtures which only use virgin materials and whether binder type will affect performance. Utilizing current design specifications, PFCs were designed with RAP contents of 0%, 15%, and 25% and four asphalt binders. These mixtures were subject to a barrage of tests which measured their ability to resist draindown, abrasion, fatigue cracking, rutting, and moisture damage. Other testing determined permeability, porosity and workability. Rutting testing employed the industry standard asphalt pavement analyzer. Fatigue cracking and moisture susceptibility testing utilized the semicircular bending test. It was determined that it is possible to design a PFC incorporating RAP which will have good performance. However, this will only be achieved when the proper materials are used. The RAP must be properly fractionated and a modified binder such as asphalt rubber or a highly modified asphalt binder (HiMA) must be used. The mixture tests combined with Life Cycle Cost Analyses demonstrated that a PFC with up to 15% RAP combined with an asphalt rubber or HiMA can provide good performance and be cost effective. Furthermore, the use of 25% RAP in combination with these binders was only limited by the asphalt rubber not meeting the specification for permeability.

Behaviour of stiffened extended shear tab connections under gravity induced shear force

Stiffened extended shear tab connections (either in full-depth or partial-depth configurations) are widely used to connect simply supported beams to the web of supporting girders or columns. Full-scale laboratory tests of stiffened extended shear tab connections underscored the differences between their observed and expected design strength calculated according to current design specifications. In particular, the design procedure of such connections neglects the influence of the out-of-plane deformation of the supporting girder web on yielding and inelastic buckling of the shear plate. These are the main governing failure modes for the full-depth configurations of stiffened extended shear tabs, when placed on one side of a supporting girder or column. The research described in this paper aims to develop a better understanding of the load transfer mechanism and failure modes of extended beam-to-girder shear tab connections. The findings are based on finite element (FE) simulations validated with full-scale experiments on beam-to-girder shear tab connections. The influence of girder web flexibility on the behaviour of single-and double-sided shear tabs is assessed. The stiffened portion of the full-depth extended shear tabs yielded due to the interaction of horizontal shear and vertical axial force. Due to the flexibility of the girder web of the single-sided shear tab, its stiffened portion experienced much larger vertical axial force in comparison to that of the double-sided configuration.

Investigation on Ultimate Strength of STS304L Stainless Steel Welded Connection with Base Metal Fracture Using Finite Element Analysis

Many studies on the application of stainless steels as structural materials in buildings and infra-structures have been performed thanks to superior characteristics of corrosion resistance, fire resistance and aesthetic appeal. Experimental investigation to estimate the ultimate strength and fracture mode of the fillet-welded connections of cold-formed austenitic stainless steel (STS304L) with better intergranular corrosion resistance than that of austenitic stainless steel, STS304 commonly used has carried out by authors. Specimens were fabricated to fail by base metal fracture not weld metal fracture with main variables of weld lengths according to loading direction. All specimens showed a block shear fracture mode. In this paper, finite element analysis model was developed to predict the ultimate behaviors of welded connection and its validity was verified through the comparison with test results. Since the block shear behavior of welded connection due to stress triaxiality and shear-lag effects is different from that of bolted connection, stress and strain distributions in the critical path of tensile and shear fracture section were investigated. Test and analysis strengths were compared with those by current design specifications such as AISC, EC3 and existing researcher’s proposed equations. In addition, through parametric analysis with extended variables, the conditions of end distance and longitudinal weld length for block shear fracture and tensile fracture were suggested.