A Summary of Changes and Derivation of LRFD Bolt Design Provisions

A statistical survey was made for a broad sample of mill test reports (MTR) of plate grades typically used in building construction including A36, A572, A588, A852, and A514 steels. Tensile properties, impact properties, and chemical compositions were analyzed. The tensile statistics agreed with assumptions made in the development of the AISC Load and Resistance Factor Design Specification for Structural Steel Buildings (LRFD Specification) (AISC, 1999). The yield-tensile ratios varied from 0.61 to 0.94, following the typical trend of increasing yield-tensile ratio with increasing strength level. The mean CVN values at 70ºF were generally over 100 ft-lbs. for all the steels, which is attributable to the fact that the toughness data were generally reported for product with specified minimum values. The minimum CVN values at 70ºF all met or exceeded the 20 ft-lbs. value specified by AISC for plate material over 2 in. thick used for built-up cross sections spliced with complete-joint-penetration groove welds and subjected to tension. The statistical analysis of composition generally indicated good weldability, particularly for A36 and A572 Grade 50.

The AISC LRFD specification (LRFD, 1999) for the design of steel structures contains provisions for what is customarily termed block shear. Notionally, this refers to the displacement of a block of material. It is usually associated with bolted details because a reduced area is present in that case, but in principle it can also be present in welded details. This paper deals only with bolted connections, however. This examination has identified that use of the LRFD Specification rules for block shear leads to conservative designs for gusset plates, non-conservative designs for coped beams, and satisfactory results for angles. Importantly, in most cases these rules do not reflect the mode of failure observed in the tests.

The 2010 AISC Specification for Structural Steel Buildings has expanded the scope in Chapter K ("Design of HSS and Box Member Connections"�) with a new Section K4, "Welds to Branches."� This paper describes the background to this development and examines the structural reliability of the weld effective length provisions contained therein. The latter is achieved by using a database of 31 welded square/rectangular hollow structural section (HSS) K-, T- and cross- (or X-) connections in which all test specimen failures were reached by fracture of the welded joints. The potential inclusion (or exclusion) of the sin θ effect, whereby fillet weld capacity is increased for loading not parallel to the axis of the weld, has also been investigated. In conclusion, some design examples are given to illustrate the weld design method, performed to the 2010 AISC Specification in both LRFD and ASD.

Numerical Study on Lateral-torsional Buckling of Honeycomb Beam

The 2022 edition of the AISC Specification for Structural Steel Buildings allows member and system instability effects to be accounted for by using advanced analysis methods that model these effects directly or through the use of the B1 (P-δ) and B2 (P-Δ) multipliers. For compression members subject to end moments only, the B1 multiplier is expressed as a function of the smaller to larger end moment ratio. This ratio is taken as positive when the member bends in reverse curvature and negative when it bends in single curvature. This code equation for B1 often overestimates the P-δ effect for double curvature bending under a high axial force but underestimates the P-δ effect for single curvature bending under almost all values of axial force. The reason for the overestimation is because the derivation of the B1 equation uses the equivalent moment concept and ignores the actual location where the maximum moment occurs in the member. When this condition is taken into consideration, it is shown herein that the equation is no longer applicable for members bent in reverse curvature under any value of axial force. The reason for the underestimation is because the effect of axial force on the moment ratio is ignored. By incorporating this effect in a new equation for B1, it is shown that this underestimation is drastically reduced. The validity of this proposed B1 multiplier is established by comparison with the corresponding theoretical values.

Tests and numerical study of ultra-high strength steel columns with end restraints

In late 2005, the American Institute of Steel Construction issued its most recent Specification for Structural Steel Buildings (ANSI/AISC 360-05). This specification includes updated design provisions in both allowable strength design (ASD) and load and resistance factor design methods (LRFD), and incorporates the design provisions for hollow structural sections and single angles. Amongst the major changes are a complete revamping of the methodologies for assessing stability of framed structures, new provisions for composite columns and updated material requirements. This paper will describe the changes and highlight those of practical significance.

Companies performing international structural design work are confronted with varying requirements imposed by different standards and methodologies. This paper presents a brief comparison of stability analysis procedures for steel structures using the Eurocode 2022 and the American Institute of Steel Construction Specification for Structural Steel Buildings (ANSI/AISC 360‐22) standards. Several structural types will be investigated, ranging from those with clearly defined effective lengths to others with more ambiguous effective lengths requiring stability analysis techniques involving explicit modeling of system imperfections and member (bow) imperfections. Geometric and material nonlinear imperfection analysis (GMNIA) will be used for comparison. Through these case studies, we illustrate the practical implications of each method, highlighting key differences. Ultimately, this study aims to enhance understanding of stability analysis and inform international best practice in structural design, contributing to safer and more efficient engineering solutions.

A large boiler support structure for a coal-fired power plant in Australia was designed by a structural engineer in the United States. Approximately 9,000 tons (8,181 tonnes) of structural steel for this project was supplied from a steel fabricator in China, using shop drawings prepared by an American detailing firm. A registered professional engineer from the designer's Australian offices supervised the work in the United States to ensure compliance with local codes and standards. Member sizes were selected from ASTM shapes, using the provisions of the Australian Standard for steel structures AS4100 (Council of Standards, 1998). However, to expedite steel delivery, it was decided to allow the detailing firm to prepare connection designs using the American Institute for Steel Construction's (AISC), Specification for Structural Steel Buildings—Allowable Stress Design and Plastic Design (ASD) (AISC, 1989). Demonstrating the compatibility of connection designs prepared using these two methods highlighted the unique difference between simple code compliance, and the art of connection design. The intent of this study is not to establish the appropriate limit states for a clip angle connection. There are numerous references that deal with this topic (Birkemoe and Gilmor, 1978; Munse, Bell and Chesson, 1959). The purpose is also not to demonstrate that one country's design approach is either superior to or less conservative than that of another country. What has been shown is that, given a structural design problem as common as a clip angle, two different approaches to engineering, based on training and experience, can interpret relatively similar design specifications, to produce significantly different results.

The moment-gradient factor in lateral–torsional buckling on inelastic castellated beams

The 2005 American steel structures design code

To extend previous research on obtaining designs that rely on a second-order inelastic hinge analysis to demonstrate that a structure is adequate in resisting the effects of factored loads, this paper presents a study of a series of two-story planar steel frames where all columns are subjected to combinations of axial force and minor-axis bending. Inelastic designs, which are prepared to satisfy both strength and serviceability limit states requirements, are compared to designs obtained using a conventional second-order elastic analysis in conjunction with the AISC LRFD Specification. The degree of accuracy and reliability of using a concentrated plasticity analysis to model system behavior is also established. The study indicates that for a majority of the frames investigated, a second-order inelastic hinge analysis can be used effectively to design steel structures. It is also shown that in some cases a distributed plasticity analysis may be required.

The capacity of each connector type in a shear-splice type of joint is reflected by its shear strength and shear deformation characteristics. When two or more types of fasteners share the load, it is clear that it is not satisfactory to simply combine the ultimate strength of each individual fastener type. Each of the different fastening elements has a different ductility and, in general, each reaches its ultimate strength at a different value of overall connection deformation. The strength of joints that combine bolts and fillet welds that act in the same shear plane has been examined. The study has shown that the rules provided in the AISC LRFD Specification do not adequately reflect the actual strength of this type of joint. Using test results from the University of Alberta and others, expressions are presented for the capacity of the various elements that make up a bolted-welded joint. These expressions enable the capacity of a combined bolted-welded joint to be predicted with a reasonable degree of accuracy. The examination showed that transverse fillet welds do not work well in combination with bolts because of the limited ductility of the former.

Composite structures have become increasingly popular in civil engineering due to many advantages, such as light weight, excellent corrosion resistance and high productivity. However, they still lack the strength, stiffness, and convenience of constructions of fastener connections in steel structures. The most popular fastener connections in steel structures are slip-critical connections, and the major factors that influence their strength are the slip factors between faying surfaces and the clamping force due to the prevailing torque. This paper therefore examined the effect that changing the following parameters had on the slip factor: (1) replacing glass fiber reinforced plastic (GFRP) cover plates with stainless-steel cover plates; (2) adopting different surface treatments for GFRP-connecting plates and stainless-steel cover plates, respectively; and (3) applying different prevailing torques to the high-strength bolts. The impact on the long-term effects of the creep property in composite elements under the pressure of high-strength bolts was also studied with pre-tension force relaxation tests. It is shown that a high-efficiency fastener connection can be obtained by using stainless-steel cover plates with a grit-blasting surface treatment, with the maximum slip factor reaching 0.45, while the effects of the creep property are negligible.

Introduction. The article proposes a method for identifying the coefficient of torsion of a high-strength bolt in the laboratory environment. The coefficient is found by determining the relative deformation of a drawn bolt using load cells. This method requires specialized equipment and a test bench, and it can be used to study the behavior of bolts. The value of the torsion coefficient is necessary to ensure the appropriate bolt tension force, since according to current friction concepts of bolted connections involving high-strength bolts, the design behavior of a bolted connection is ensured by the appropriate bolt tension force, determined using the required torque. Otherwise, the actual behavior of a bolt differs from its design behavior, since only a pre-set tension force ensures the necessary bearing capacity of a bolted connection in the friction planes.
 
 Materials and methods. Specimens of bolts under study are made according to the German standard DIN931 with a strength of 10.9, and the size M14 × 220; their nuts comply with the German standard DIN934 with a strength of 10 and the size M14. Instron 1000HDX tension testing machine was used to make a diagram describing the performance of steel bolts. Nut tension was determined using NOGRAU NTW24-034R torque control key, and bolt elongation was controlled using FLA 5-11 strain gauges and the National Instruments data collection system.
 
 Results. A new method for monitoring the measurement of the torsion coefficient of high-strength bolts was tested and proposed in furtherance of the research conducted by the authors.
 
 Conclusions. As a result of testing, a change in the torsion coefficient can be evaluated depending on the torque value.