Beam element verification for 3D elastic steel frame analysis

The paper describes the attributes that should be possessed by a benchmark example for verifying the beam elements used to carry out 3D linear buckling analysis and 3D second-order elastic analysis of steel frames. Based on the attributes described, the paper proposes a suite of benchmark examples selected from the literature. The necessary features of a beam element required to pass the proposed benchmark problems are given, and beam elements that possess these features are cited. The paper also explains the merits of linear buckling analysis examples, and provides a commentary on two well-known examples

Cubic beam elements in practical analysis and design of steel frames

This paper discusses various issues in the use of cubic beam elements for computer structural analysis/design of steel frames. It is pointed out that the concern expressed in recent literature regarding the number of cubic elements required to model a steel member is not justified, and that the inaccuracy of one cubic element in Euler buckling analysis of a simply supported column is largely irrelevant to the second-order elastic analysis/design or advanced analysis of steel frames. The sources of inaccuracy of the cubic element are elucidated. It is also explained that the plastic-zone analysis method is not so inefficient as was previously believed. The spatial cubic element is shown to be capable of accurately accounting for the coupling between axial, flexural and torsional deformation modes. It is concluded that for the purposes of second-order elastic analysis/design and advanced analysis of 2D and 3D steel frames, the well-documented cubic element is a versatile and efficient choice

Limitations of current design procedures for steel members in space frames

The use of more advanced methods of analysis to design steel frames may lead to substantial material savings, in addition to simplicity in the design procedures. However, these benefits do not yet appear to be a powerful incentive for many structural engineers to abandon the familiar linear elastic analysis (LEA) based design procedures, even when dealing with steel structures that are not regular rectangular frames. This paper uses a heuristic example to demonstrate the serious limitations of the LEA based design procedures, whether alignment charts or system buckling analysis is used to determine the effective lengths of the compression members. It is shown that LEA based design procedures may lead to unsafe structures due to their inability to account for bending moment amplification in the rigidly connected tension members of a space frame. Furthermore, there is no allowance for the amplification of axial forces due to changes in the structure geometry, which is significant for the space frame example. Confidence in the system buckling analysis method for determining the effective lengths of compression members, based on linear buckling analysis, is shown to be potentially dangerous for certain types of frames. For the space frame example, the elastic buckling load is overestimated by over 200%. The conservatism inherent in the member capacity check equations specified in steel design standards is also illustrated

Effect of loading direction on the bearing capacity of cold-reduced steel sheets

This study is concerned with double-shear bolted connections in cold-reduced steel sheets that undergo the pure bearing failure mode of the inside sheet. Compared to the published test results of bolted connections failing in the net section fracture, those involving the bearing failure mode had very wide scatter in the ultimate test loads of specimens having seemingly similar configurations. This technical note presents the laboratory test results of 51 specimens composed of G2 and G450 steel sheets, which have very different ductility properties. One new and significant finding is that the absolute bearing capacity can be considerably higher in the rolling direction of the cold-reduced steel sheet than in the perpendicular direction, even though the tensile strength has the opposite trend. Another result is that material ductility has a much greater effect on the bearing capacity than on the net section tension capacity. It was also found that snug tightening had little effect on the bearing capacity of specimens thicker than 1.5 mm. For the inside sheet of a double-shear bolted connection, the current American Iron and Steel Institute provision for bearing capacity is reasonably accurate if the load is applied in the rolling direction of G2 steel sheet, but is overoptimistic in the perpendicular direction

Block shear capacity of bolted connections in hot-rolled steel plates

This paper extends the research previously conducted at the University of Wollongong on block shear failure of bolted connections in cold-reduced steel sheets with low ductility to hot-rolled steel plates. It examines the applicability of the basic approach employed for cold-reduced sheet steel bolted connections, which makes use of the so-called active shear planes, to hot-rolled steel plate connections. The active shear planes lie midway between the gross and the net shear planes defined in the steel structures specifications. The paper shows that shear yielding leading to the block shear failure of a bolted connection in a hot-rolled steel gusset plate is typically accompanied by full strain hardening. The paper proposes a design equation that provides more accurate and consistent results compared to the American, Australian, Canadian and European code equations in determining the block shear capacities of bolted connections in hot-rolled steel gusset plates. A resistance factor of 0.85 is recommended in order to achieve a target reliability index of 4.0 or greater

Bearing Strength of Untightened Double-Shear Bolted Connections in Cold-Formed Steel Construction

This paper presents the experimental investigation of cold-formed steel double-shear bolted connections where both the bolt head and the nut are not in contact with the outer sheets. The inner sheet of each specimen is not constrained from out-of-plane distortion or bulging downstream of the bolt, and fails in bearing. Based on a series of tests involving specimens having bolt diameters ranging from 12 to 16 mm and sheet thicknesses ranging from 1.5 to 3.0 mm, it has been found that the absence of out-of-plane constraint in untightened bolted connections leads to much lower bearing capacities than predicted by the specification’s bearing strength equation. The effect is more pronounced for thinner sheets. An interesting finding is that the threaded bolt specimens had higher bearing capacities than the corresponding ones with shank bolts. It appears that the bolt threads provided some out-of-plane constraint to the connected sheet

Combined bearing and shear-out capacity of structural steel bolted connections

This study is concerned with the strength limit state of serial bolted connections in structural steel plates. It points out that the ultimate load capacity of a serial bolted connection failing in combined bearing and shear-out cannot be computed as the simple sum of the respective ultimate bearing and ultimate shear-out capacities, which is implicitly permitted in design specifications worldwide. Based on the laboratory test results of 10 hot-rolled steel plate specimens composed of three different grades with nominal thicknesses ranging from 5 to 8 mm, the paper first establishes the ultimate bearing coefficient of a 20-mm bolted connection in a structural steel plate to be 3.5. Coupled with the shear-out equation previously derived, a design equation where the shear-out capacity of the downstream bolt varying quadratically with the end distance is then proposed to determine the combined bearing and shear-out capacity. The proposed equation is demonstrated through verification against independent laboratory test results involving 5-mm plates of three different grades to be significantly more accurate than the simple sum. Explanation for the unexplained results obtained by another researcher using his own equation is provided in this paper

Strength and Behavior of Fillet Welded Connections in G450 Sheet Steel

G450 steel to AS 1397 is a cold-reduced sheet steel with in-line galvanizing. Its grade is 65 ksi (450 MPa) yield and 70 ksi (480 MPa) tensile strength. It is widely used in Australia for purlins, and is being used to fabricate light-weight Portal frames, often by welding. The effect of welding on G450 sheet steel in the heat affected zone was unknown and so the project was performed to investigate the strength of fillet welded connections. Transverse and longitudinal fillet welded connections in 0.06 in (1.5 mm) and 0.12 in (3.0 mm) sheet steels were tested to failure. The failure modes and ductility of different types of connections are described. The test results are used to check the design rules in the AISI Specification (Section E2.4) and the Australian/New Zealand Standard for Cold-Formed Steel Structures AS/NZS 4600 (Clause 5.2.3). Recommendations are made for revised capacity factors. The quality of fillet welded connections in thin sheet steels produced by industry fabricators is investigated. The need to complement the macro test with the destructive prying test as part of the pre-qualification procedure for such connections is demonstrated

Block shear failure planes of bolted connections - direct experimental verifications

This paper presents direct experimental verifications of the active shear planes in bolted connections, previously identified by the first author for determining the block shear capacity. The laboratory test results were obtained by independent researchers for specimens where the applied loads were resisted by the block in shear only. The first set consists of five bolted connection specimens in the webs of wide flange sections where the tensile resistance planes had been sawn off. The second set consists of ten bolted connection specimens each in one leg of an angle section that had fractured completely along the net tensile plane through a block shear failure. Comparisons among the gross, net, and active shear planes against the independent laboratory test results showed that the critical shear planes of bolted connections were best represented by the active shear planes rather than either the gross or the net shear planes. It is also pointed out that full or almost full shear strain hardening was generally achieved at the ultimate limit state of block shear failure of bolted connections in hot-rolled steel plates or sections, irrespective of the connection length. Verification against independent laboratory test results of tee sections bolted at the web reinforces this point

A buckling model for the stability design of steel columns with intermediate gravity loads

This paper points out an accurate buckling model for determining the flexural effective length of a steel column subjected to intermediate gravity loads, for applications in the 2D second-order elastic analysis based design procedure. The proposed buckling model has notional horizontal restraints where equivalent horizontal forces have been applied, and can be readily programmed into a structural analysis/design software. Thirty columns having various end restraints and subjected to concentrated gravity loads within their unsupported lengths are analysed to demonstrate the merits of the proposed buckling model. It is shown that, in most of the cases analysed, the proposed buckling model leads to more liberal column capacities compared to the use of the unity effective length factor or the buckling model described in the European drive-in rack design code. The more liberal capacities are very close to the ultimate loads determined through second-order plastic-zone analysis