bluuebunny/crossref_metadata_2025 huggingface dataset:
A Practical Approach to the Leaning Column
Authors: Geschwindner Louis F.
Published: April 2024

The "leaning" column has existed as an element in steel structures from the time steel frames were first constructed. The simplest form of a leaning column is a pin-ended column which has no lateral stability of its own; thus, it relies on other parts of the structure to provide for its lateral stability and the lateral resistance for the entire frame. The impact of leaning columns on the lateral stability of the unbraced frames to which they are attached must be accounted for in design. This paper will look at practical ways to account for leaning columns through the use of K-factors in both LRFD and ASD design. It should be clear that the leaning column is a consideration that results from the structural framing, not from the use of ASD or LRFD. It is also clear that accounting for the total lateral resistance in a frame may lead to reduced column sizes with their accompanying savings. Although the Yura approach does, for some conditions, give what appears to be overly conservative results, it can readily be modified to yield the Lim & McNamara approach which provides sufficiently accurate results for design. This was shown even for those cases reported in the literature for which the Yura approach is overly conservative.
An Assessment of K Factor Formulas
Authors: Shanmugam Nandivaram E. , Chen Wai-Fah
Published: April 2024

Current structural design practices recognize that the maximum strength of frames and the maximum strength of component members are interdependent, but it is not practical to take this interdependence into account rigorously. This reasoning lends support to the Structural Stability Research Council (SSRC) technical memorandum which states that "in design practice, the two aspects, stability of individual members and elements of the structure and stability of the frame system as a whole, be considered independently." However, it is admitted that "difficulties are encountered in complex frameworks when attempting to compensate automatically in column design for the instability of the entire frame." Considerable attention has been paid in the literature to the study of different types of frame elements such as compression members, beams, bracing system and connections and also their effects on the stability of the frame and as a result, several methods have been proposed for evaluating the frame strength. However, the effective length concept for evaluating the frame strength is the most popular method for estimating the interaction effects of a framed member on the total frame stability, and it is recommended by almost all the current specifications.
Influence of Cross Frames on Load Resisting Capacity of Steel Girder Bridges
Authors: Azizinamini Atorod , Kathol Steve , Beacham Michael W.
Published: April 2024

The fifteenth edition of the AASHTO manual requires intermediate cross frames in steel girder bridges with maximum spacing of 25 feet. Although these cross frames may be needed for temporary loads their effectiveness following construction has been a point of debate for short and medium span bridges. Cross frames with different configurations have been utilized in bridge construction. Besides increasing construction costs, many problems in steel girder bridges could be attributed to the presence of cross frames. For instance many states have observed cracking in the girder web of bridges in the vicinity of the cross frame's connection to the beam, especially for details where stiffeners are not rigidly connected to top and bottom flanges.Prior to casting the concrete deck, smaller spacing of cross frames results in smaller laterally unbraced lengths of steel girders and, consequently, could result in smaller sections. In some steel bridges it is therefore possible to have diaphragm spacing of less than 25 ft., the maximum spacing allowed by the AASHTO manual. The need for cross frames in these instances becomes an even more serious question, especially if their presence results in unsatisfactory performance of the bridge (such as developing cracking in girder web). To address this issue, a combination of analytical and experimental investigations was conducted. A summary of the experimental investigation related to the use of cross frames is presented in this paper.
Prestressed Steel Girders for Single Span Bridges
Authors: Snyder Russell D.
Published: April 2024

Long single span bridges are becoming more common on today's highway systems. The span lengths of these bridges grow as the widths of the underlying roadways increase to accommodate larger volumes of traffic and the use of intermediate supports in the underlying median are discouraged to allow for future widening of the roadway or mass transit corridors. Span lengths of 150 to 250 feet are not uncommon and typically require the use of steel plate girders. Since these simple spans have no benefit of continuity at the supports, the required plate sizes tend to be rather large. One method to reduce the size of the plates and thus the overall amount of steel needed for each girder is prestressing. Just as the load carrying ability of a concrete beam is enhanced by the application of prestressing, the required size of a steel girder may be reduced in comparison to its conventional counterpart. Prestressed steel girders are not a new idea, in fact eastern European designers have used prestressed steel girders for quite some time. The major application in the United States has been in the area of bridge rehabilitation. This paper summarizes the economic advantages of utilizing prestressed steel girders for proposed single span bridges by comparing conventionally designed girders to prestressed girders. The comparative analysis will report differences in material usage and will discuss the effects of the differential cost of construction and the intangible benefits of the prestressed girder alternative.
A Closer Examination of the Axial Capacity of Eccentrically Loaded Single Angle Struts
Authors: Lutz Leroy A.
Published: April 2024

The purpose of this article is to address the axial capacity evaluation of eccentrically loaded single angles. The focus will be to examine and expand on the axial capacity evaluation made in Example 3-8 of the 1993 LRFD Manual. The Example as presented did not illustrate the less conservative approach permitted by the Specification for Load and Resistance Factor Design of Single-Angle Members. The evaluation of the axial capacity with due consideration of the sign of the stress is addressed. Also, since the example is supposed to represent the capacity obtained by load from a gusset plate attached to one leg, an examination of this situation is made.
Fatigue Life of Double Angle Tension Members
Authors: Stallings J. Michael , Cousins Thomas E. , Christopher Bradley P.
Published: April 2024

Alabama Department of Transportation (ALDOT) bridge inspectors discovered failed (cracked) filler plate welds in numerous double angle tension and compression members of the floor trusses of twin tied arch bridges on Interstate 1-65 in late 1990. A typical double angle truss member with a cracked filler plate weld is illustrated. The ends of the filler plates are attached to the back to back legs of the double angles with square groove welds. The welds are approximately two inches long (full width of filler plate) and are ground flush with the outside ends of the filler plates. Based on field test data, the four outer diagonals were found to be the most highly stressed members in the floor trusses. For these four members, the nominal extreme fiber stress ranges near the filler plates due to axial load plus bending varied from 5 to 29 percent higher than the axial stress ranges. The percentage increases in stresses due to bending in these members was found to be unaffected by truck weight or lane position.
Improved Shear Strength of Webs Designed in Accordance with the LRFD Specification
Authors: Bradford Mark A.
Published: April 2024

The dependence of the LRFD design rules for shear resistance on the web elastic local buckling coefficient is demonstrated. A finite strip method of analysis, based on complex arithmetic and that incorporates shear, is then used to derive elastic local buckling coefficients that incorporate the restraint provided by the flanges of an I-section member. It is shown by an example how these enhanced buckling coefficients lead to greater calculated shear strengths, thereby producing economies in the use of steel.
The Effect of Eccentricity on Brace-to-gusset Angles
Authors: Thornton William A.
Published: April 2024

Claw angles are used in many bracing connections as shown in Figure 1. Normally these angles and their connections are designed for direct load only without consideration of the fact that the connections are to opposite legs of the angles and of the eccentricities thereby induced. It is the purpose of this note to demonstrate that this practice is generally acceptable, and to produce some guidance as to when it is not.
Ultimate Strength Considerations for Seismic Design of the Reduced Beam Section (Internal Plastic Hinge)
Authors: Iwankiw Nestor R.
Published: April 2024

Several international (Ref. 1-4) and more recent US (Ref. 5 & 6) research tests have confirmed that the use of a reduced section (often referred to as "dogbone") of a wide flange beam in the proximity of welded beam-to-column moment connections is a very promising means to improve seismic ductility. The notion to protect against seismic overloads through an intentional ductile "fuse" has long existed, but this particular application has recently surfaced as an alternative solution to the post-Northridge concerns about the prescriptive welded connection detail. ARBED, the owner of a 1992 US patent on the reduced beam section (RBS), has graciously waived any commercial royalty rights for its public use. The RBS is accomplished through an engineered gradual transition of the beam flanges to the intended reduced section at a given location. In comparison to the reinforced (strengthened) connections with beam cover plates, ribs, side plates, or haunches, this modification provides the more reliable ductility of "interior" plastic hinge formation in the main beam member but without elevating force demands on the supporting columns and the remaining framing system beyond those of the original member sizes. Likewise, this efficient configuration does not increase the required weld deposition volume, constraint, nor supplementary material requirements. This paper outlines several basic strength principles that could be used in a convenient design of beams with reduced sections to achieve a proper balance between seismic ductility and strength demand. First-order effects of moment continuity, beam span, and beam properties were included in a general systematic procedure.
Design of Crane Runway Beam with Channel
Authors: Ellifritt Duane S. , Lue Dung-Myau
Published: April 2024

A common practice in industrial buildings is to weld a channel, open side down, to the top flange of a standard rolled beam for use as a crane runway. In many cases, it is not possible to brace a crane runway laterally between columns, so the channel provides additional lateral stiffness. There are several interesting structural questions associated with the practice, like, what should be the welding pattern? How are the residual stresses affected? What if the channel has a yield strength different from the beam? However, the primary question addressed in this paper is, how does one check such a beam for lateral-torsional buckling?
The Ultimate Strength of Symmetric Beam Bolted Splices
Authors: Sheikh-Ibrahim Firas I. , Frank Karl H.
Published: April 2024

Rolled beams or plate girders are often spliced for a variety of reasons, such as: the required full length may not be available from the mill, the designer may desire a change in the cross section of the beam, or the fabricator might find it economical to splice the beam at certain locations to reduce shipping lengths or lifting loads. Figure 1 shows a typical bolted beam splice. A beam splice must transfer the shear and moment of the beam at the location of the splice. However, the exact distribution of shear and moment between the web and flange splices is not known. Figure 2 shows a free body diagram taken by cutting the splice through its centerline. Figure 2 shows that the flange splices carry tension or compression and possibly a portion of total shear. It also shows that the web splice carries predominantly the shear and possibly a portion of total moment at the splice.
K-factors for Unbraced Frames: Alignment Chart Accuracy for Practical Frame Variations
Authors: Roddis W.M. Kim , Hamid Hazlan Abdul , Guo Chelsea Q.
Published: April 2024

For design of steel columns in unbraced frames, the current AISC specification commentaries from both LRFD and ASD contain an alignment chart to determine the K factor for a particular column. The K factor is based on the effective length concept where K factors are used to equate the strength of a compression member of length L to an equivalent pinended member of length KL subjected to axial load only. The unbraced frame alignment chart is a graphical representation in nomograph form of a transcendental equation of a buckling solution of a subassemblage. This solution involves several assumptions not necessarily satisfied in a particular practical situation. The goals of this paper are to point out the practical limitations of the unbraced frame alignment chart effective length approach and to encourage the use of story-based effective length factors. This is done in the following manner. A parametric study shows the limits of accuracy and applicability of the unbraced frame alignment chart results from a linear buckling analysis. The benefits of the AISC Commentary equation C-C2-5 story-based effective length factor are shown through comparison to the alignment chart and linear buckling analysis results. The parametric study shows sufficient examples to encourage practitioners to use story-based techniques for stability assessment. The parametric study investigates variations in bay width, column moment of inertia, loading, and column height. All nomograph results reported include correction of girder factors to account for unequal girder end moments with noncenterspan inflection point. The alignment chart performance is relatively insensitive to bay width variation. Variations in column moment of inertia and column loading lead to large inaccuracies in the alignment chart K factor values but C-C2-5 better handles these cases. The alignment chart performance is most sensitive to column height variation. Configurations with large variation in column height require frame stability analysis to obtain accurate K factors.
Experimental Investigation of Dogbone Moment Connections
Authors: Engelhardt Michael D. , Winneberger Ted , Zekany Andrew J. , Potyraj Timothy J.
Published: April 2024

A test program was conducted on seismic-resistant steel moment connections constructed using a Reduced Beam Section, also known as a "dogbone." In the dogbone connection, portions of the beam flange near the beam-to-column connection are trimmed in order to enhance ductility under severe cyclic loads. This test program was conducted in order to evaluate the dogbone connection for use in a 25 story steel office building in Salt Lake City. A total of five large scale specimens were tested in this program, with beam sizes ranging from W30X148 up to W36X194. The specimens combined the dogbone cutout in the beam flanges with an all welded beam-to-column connection constructed using improved welding practices. The test program showed excellent performance for specimens constructed with a circular radius cut dogbone. Cost comparisons indicated that this connection also provided good economy compared to other alternatives considered for this building construction project. Overall, the dogbone appears to be one of the more promising moment connection details for use in seismic-resistant steel moment frames. This paper summarizes the results of the experimental program, and provides suggestions for the design of dogbone moment connections.
Experimental Implementation of Active Control to Reduce Annoying Floor Vibrations
Authors: Hanagan Linda M. , Murray Thomas M.
Published: April 2024

When excessive levels of floor vibration disturb the occupants or impair the function of a facility, repair measures are often sought. This paper discusses the role of damping and the application of active control in reducing unacceptable floor motion. The practical implementation of active control, using an electromagnetic force actuator in a computer controlled velocity feedback loop, is also described. Finally, experimental results for two temporary installations, an office floor and a chemistry laboratory floor, are presented to illustrate the effectiveness of the active control scheme.
Semi-Rigid Frame Design Methods for Practicing Engineers
Authors: Christopher John E. , Bjorhovde Reidar
Published: April 2024

Design of semi-rigid (PR) frames focuses on behavior characteristics of non-linear connections, including their substantially different loading and unloading characteristics. Moment-rotation connection representations, such as the three-parameter power model, facilitate the calculation of stiffness data required for frame analysis. In this paper, the connection characteristics are described in terms of linearized connection stiffnesses that are calculated on the basis of expected connection loads. This allows for the use of first-order analysis to determine structural stability, serviceability and member load effects. The design method detailed in this paper includes the concurrent selection of connection and member sizes. The LRFD approach of AISC is utilized, including the provisions that rely on amplification factors to account the provisions that rely on amplification factors to account for second-order effects. Member section checks are made with unbraced length K-factors determined from the alignment charts, using modified relative distribution factors to account for connection deformation
Spliced Axially-Loaded Single-Angle Members in Compression
Authors: Sakla Sherief S.S. , Wahba Yohanna M.F. , Madugula Murty K.S
Published: April 2024

Due to construction and transportation considerations, angles used as leg members in latticed towers are often joined together in the field using bolted splice plates. In many instances, the centroid of the angle cross section does not coincide with the centroid of the splice plates used to connect the angles. It is not known what effect such a splice has on the compressive ultimate load carrying capacity of the single-angle member. Reseach results on spliced angle specimens of low slenderness ratio (fabricated according to the communication tower industry practice) and one reference specimen of the same size and length are reported herein and compared with AISC-LRFD Specification. It is shown that the ultimate load carrying capacity of spliced specimen was, on the average, 8 percent less than that of the reference specimen.
Developments in Long Span Composite Slabs
Authors: Widjaja Budi R. , Easterling W. Samuel
Published: April 2024

Composite slabs constructed using cold-formed steel deck are by far the most common forms of floor used in steel-framed buildings in the United States. Indeed it is largely due to the attributes that steel deck provides that make steel-framed buildings as economically competitive as they are. The maximum unshored span, using composite deck profiles manufactured in the U.S., is approximately 15 ft. However, the use of 16 ga deck and lightweight concrete is required to achieve 15 ft unshored clear spans. This number depends on the deck cross section as well as the concrete thickness and unit weight. Typically, deck spans in the range of 8-10 ft are used. The choice of unshored construction is common because of the savings in construction cost and time. If the typical span lengths can be increased by a factor of say 1.5 to 2, significant cost savings can be expected because of the reduction in the number of filler beams and their connections to the girders. The cost of the steel deck will increase, however the savings realized by using fewer filler beams will be greater than this increase. The advantage stems largely from cost savings in fabrication and erection of fewer members and connection of those members.
Examination of AISC LRFD Shear Lag Design Provisions
Authors: Kirkham William J. , Miller Thomas H.
Published: April 2024

Steel structures are often assembled from standard steel shapes connected by welds or other fasteners. Sometimes, a number of bolts or welds are used to connect all the elements (flanges, web, etc.) of a member to the elements of another member. In most structures, however, not all of the elements of a given cross-section are connected, for numerous reasons. When some elements of a member are not connected, shear lag may result. Typically, in cross-bracing of trusses and frames, an engineer determines the geometry, strength and economical design of the connections between major load-carrying members, joined by one or more gusset plates. When the braces enter the joint at an angle, often little clearance is available to effectively attach the web of the brace. The sizing of this bracing member is determined in part by the efficiency of directly connecting only the flanges to the gusset plates.
A Technical Note: Derivation of the LRFD Column Design Equations
Authors: Tide Raymond H.R.
Published: April 2024

Since the publication of the first Load and Resistance Factor Design (LRFD) Specification by the American Institute of Steel Construction, Inc. (AISC, 1986) the column design equations have been presented by the Euler buckling equation in the elastic range and an exponential equation in the inelastic range. Background information, including accumulated test data, for these equations was presented at a Structural Stability Research Council (SSRC) meeting held in Cleveland, Ohio in 1985 (Tide, 1985). However, the actual derivation of the design equations relative to the accumulated test data has not been documented. The purpose of this paper is to document the derivation of the LRFD column design equations. LRFD column equations were derived to represent a lower bound to the available test data and to satisfy the philosophical requirements of nearly all of the AISC Specification committee members at the time. Slight numerical differences occur at the common point for the two equations for both the non-dimensional stress and slope.
AISC LRFD Rules for Block Shear in Bolted Connections—A Review
Authors: Kulak Goeffrey L. , Grondin G.Y.
Published: April 2024

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.
Tension Field Action in Hybrid Steel Girders
Authors: Barker Michael G. , Hurst Austin M , White Donald W.
Published: April 2024

With the advent of HPS70W (70 ksi) steel, several bridges have been built, and many more will be built, using hybrid design provisions. One limit with hybrid girder design, which decreases the beneficial aspects, is that tension field action (TFA) is not allowed when determining the shear capacity. This is a severe shear capacity penalty for using hybrid girders. This paper proposes that tension field action should be allowed for hybrid girders and presents a modified moment-shear interaction. Hybrid tension field action would allow shear capacities well above what is currently allowed by AASHTO. With an increase in shear capacity, fewer transverse stiffeners will be necessary. A decrease in stiffeners allows for a more economical design of hybrid plate girders, substantial cost savings in material and fabrication and fewer fatigue details. The paper also presents planned experimental and finite element studies that are expected to verify the development of tension field action in hybrid girders and the capability of the proposed modified moment-shear interaction equation as a lower bound strength estimate.
Errata: The Effects of a Severe Fire on the Steel Frame of an Office Building
Authors: Dexter Robert J. , Lu Le-Wu
Published: April 2024

Errata
Using Moment and Axial Interaction Equations to Account for Moment and Shear Lag Effects in Tension Members
Authors: Epstein Howard I. , DAiuto Christopher L.
Published: April 2024

Shear lag effects and moments reduce the strength of structural steel tension members. This shear lag exists when connections to tension members transmit the load through some, but not all, elements of the member (legs of an angle, web and flanges of a Wor tee, etc.) and may result in an eccentrically loaded connection. Recent research on structural tees at the University of Connecticut has shown that the moment produced by eccentric loading depends upon the connection geometry as well as the rotational stiffness of the connection. Once the moments in tension tees and other sections are found, these members may be more correctly and safely designed by accounting for the interaction of bending moment and axial force, instead of the empirical shear lag factors. The rotational stiffness of the connections is shown to be an important design consideration.
The Effect of Bedding Layer on the Strength of Shear Connection in Full-Depth Precast Deck
Authors: Kim Jong-Hee , Shim Chang-Su , Matsui Shigeyuki , Chang Sung-Pil
Published: April 2024

Shear connection in a steel-concrete composite bridge with a full-depth precast deck is characterized by the material properties of the non-shrink mortar, which is the filler in the pockets for the shear connectors, and the existence of a bedding layer between the precast deck and the steel girder. As a consequence, the behavior of the shear connection is very different from that of the more widely used cast-in-place concrete deck. Experiments on push test specimens with several parameters varied, such as the cross-sectional area of the stud connectors, the compressive strength of the mortar, and the thickness of the bedding layer, were performed to evaluate the ultimate strength of the shear connection in the precast deck. The test results have shown that the effect of the compressive strength of the mortar on the ultimate strength of the shear connection is insignificant within the limit of these tests. The ultimate strength of the shear connection decreases considerably with an increase of the bedding layer thickness. An empirical equation for the ultimate strength of the shear connection considering the effect of the bedding layer thickness is presented in this paper. Based on the results, recommendations for the design of the stud shear connection in a full depth precast deck are suggested.
Technical Note: Torsional Analysis of Steel Sections
Authors: Moore II William E. , Mueller Keith
Published: April 2024

Torsional analysis of rolled steel sections is generally accomplished with torsional function curves which have been published by the American Institute of Steel Construction in Design Guide No. 9, Torsional Analysis of Structural Steel Members (Seaburg and Carter, 1997), which is an update to an earlier Bethlehem Steel publication (Heins and Seaburg, 1963). Such problems are more easily solved with a personal computer than with charts, and this paper presents the equations in a form suitable for programming.
Closure: AISC LRFD Rules for Block Shear in Bolted Connections—A Review
Authors: Kulak Goeffrey L. , Grondin G.Y.
Published: April 2024

Closure
Discussion: AISC LRFD Rules for Block Shear in Bolted Connections—A Review
Authors: Gupta Mohan , Gupta L.M.
Published: April 2024

Discussion
Torsion in Closed Sections
Authors: Siev Avinadav
Published: April 2024

Academic discussions of torsion in closed sections can be found in most textbooks on elasticity; however, there is a notable lack of literature containing an engineering approach to this subject. This may be due to the fact that, until recently, pipes were the only closed sections commonly used in engineered structures. With the increased use of welding, and with developments such as "orthotropic" steel bridge decks, closed sections will undoubtedly be encountered more frequently in engineering practice. This paper will discuss the analysis of torsion in closed sections from an engineering point of view. Emphasis is placed on the physical significance of equations, rather than exact theoretical proofs. It is hoped that this treatment will lead to a better understanding of the engineering aspects of the subject.
Torsion of Rolled Steel Sections in Building Structures
Authors: Hotchkiss John G.
Published: April 2024

Torsional stress in a steel framed building are rarely serious enough to require design analysis. Many torsional situations can be disregarded completely. There are conceivable conditions, however, in which torsional loads can produce stresses of sufficient magnitude to require torsional analysis of a framing member. It is important, therefore, that the structural engineer understand the principles of torsional behavior in rolled steel sections, and be able to recognize those special situations in which torsional loading may be significant to the design. The purpose of this paper is to provide practical guidance to the designer in the evaluation and analysis of the effects of torsional loading on steel framing members. Design examples illustrate both a "short" approximate method of torsional analysis and a more exact method. A brief review of basic torsional theory and the torsional properties of rolled steel sections are included.
Stresses and Displacements in Three-Dimensional Trusses
Authors: Kushman Robert L. , Geer Elihu
Published: April 2024

A method is already available for the direct solution for stresses and displacements in three dimensional trusses. The method merits consideration by structural designers. No analogies are used. A checkerboard system of trusses is not necessary. Indeterminacy does not add in the least to the difficulty of solution, and in fact does not even have to be known. The end product is maximum stress in each member for any combination of possible loads. Moreover, the method works even better for planar trusses. The principal disadvantage of this method is the larger number of unknowns—three for each joint which can displace. However, this feature is no handicap to the digital computer. It merely highlights the need to use the computer. A fairly sophisticated computer can solve a hundred simultaneous equations in three minutes. A modern structural design office cannot afford not to have access to a computer facility.
Column Stability in Type 2 Construction
Authors: De Falco Fred , Marino Frank J.
Published: April 2024

Analysis of the stability of columns has become of increasing importance under the impetus of the AISC Specification. The discussion of "effective length" contained in the AISC Commentary makes reference to columns in continuous frames classified as Type 1 construction in the AISC Specification. Described herein is a method whereby the Commentary discussion is extended to include structures commonly designed as simply framed (Type 2 construction), but which rely upon the connection for frame action to resist lateral forces. The alignment chart provided by the Column Research Council offers a rapid and convenient method for evaluating the K factor for columns with rigid beam connections. Where structural connections are partially rigid, modification to this procedure must be made. Figure 1 illustrates the relationship between the deflected shape of the column and its effective length. Any additional rotation of the top of the column because of the incomplete (partial) rigidity of the connection increases the effective length. This is indicated in Fig. 1a by the higher position of the intersection of the extension to the elastic curve and the projection of the undeformed column axis.
Lehigh Conference on Plastic Design of Multi-Story Frames-A Summary
Authors: Driscoll Jr
Published: April 2024

In August, 1965, a conference of teachers of structural engineering and practicing structural engineers was held at Lehigh University. The purpose of the conference was to present a comprehensive coverage of new developments in the application of plastic design principles to the design of steel multi-story building frames. The conference consisted of a group of basic lectures and experimental tests performed by members of the Lehigh staff and additional supplemental lectures by outstanding engineers and educators who were attending the conference. This paper will give an outline of the plastic design procedures proposed with specific detailed coverage on some key new developments. The scope of the conference covered rigid frameworks considered as single plane structures in which sway was resisted either with the aid of diagonal Xbracing or by rigid frame action alone. An essential part of the conference was a comprehensive set of lecture notes and a design aids booklet which will serve as the primary references for this paper.
Experimental Investigation of Reduced Beam Section Connections by Use of Web Openings
Authors: Won Park Jong , Hwang In Kyu
Published: April 2024

Since the 1994 Northridge Earthquake, a wide variety of different moment connections have been developed to provide high ductility and reliable performance. Most of these moment connections incorporate the reinforcement at the connection using cover plates, ribs or haunches (Engelhardt, Sabol, Aboutaha, and Frank, 1995; Engelhardt and Sabol, 1998; Uang and Bondad, 1996; Uang, Bondad, and Lee, 1998; Whittaker and Gilani, 1996). The purpose of the reinforcement at the connection was to force the plastic hinge away from the face of the column, where premature fractures can occur due to potential weld defects, stress concentrations, etc. The reinforced connections generally showed good performance. However, reinforcing the connection may increase its fabrication costs. Moreover, there were some concerns with respect to reliability resulting from the very large weld for reinforcement. A total of six large-scale tests were performed on single cantilever type test specimens. The specimens were subjected to slowly applied cycles of loads. A test program was conducted on Reduced Beam Section connections by use of beam web openings. The test specimens showed good performance overall, although yielding occurred at lower levels of rotation and strength degradation was worse than for reduced beam flange type connections (dogbone connections).
Design of Single Angles Bent About the Major Principal Axis
Authors: Earls Christopher J.
Published: April 2024

Hot rolled steel angles are frequently used in applications wherein their flexural strength must be quantified. While flexural applications of angle members frequently involves bending within the plane of one of the angle legs, other bending scenarios can arise. One other similar scenario involves bending a single angle member about its major principal centroidal axis as shown in Figure 1. A practical example of when this type of bending may occur involves the case of sign and billboard structures in which an equal leg single angle member may be specified for the girts that support the face of the sign. The effects of gravity loading from the face of the sign result in major axis bending of the girts. In such instances it is obviously important to understand the major axis strength characteristics of the single angle members. \Nonlinear finite element modeling techniques have been employed herein for the study of equal-leg, hot-rolled steel single angle members bent about the major principal centroidal axis. Results from the modeling indicate that a lower bound design approach can be encapsulated in the form of two, linear, nominal moment predictive equations that depend on the angle leg slenderness and the angle beam overall slenderness.
Behavior of Built-Up Shear Links Under Large Cyclic Displacement
Authors: Itani A.M. , Elfass S. , Douglas B.M.
Published: April 2024

The towers of the Richmond-San Rafael Bridge (RSRB) play a significant role in the overall bridge seismic behavior and performance. They are responsible for transferring the inertia forces that are generated in the superstructure to the foundation during an earthquake. Therefore, the components of these towers lie in the direct seismic load path and thus any premature failure in these members will interrupt the load path causing inadequate seismic behavior. This paper summarized the results of an experimental investigation of two built-up shear links. As expected, the shear dominated the behavior of the two built-up links. The plastic rotational capacity for the two links exceeded the code specified values for such configurations.
Lateral-Torsional Buckling of Wide Flange Cantilever Beams
Authors: Dowswell Bo
Published: April 2024

The American Institute of Steel Construction, Load and Resistance Factor Design Specification for Structural Steel Buildings includes provisions for the design of beams to prevent lateral-torsional buckling. The design method uses an equation that was derived for a simply supported beam with equal end moments. The equation is not accurate for cantilever beams because the mechanics of buckling are different from simply supported beams. The AISC procedure produces over-conservative results for cantilever beams that are braced laterally at the tension flange, and unsafe results for cantilever beams that are braced laterally at the compression flange. Equations to predict the lateral-torsional buckling capacity of cantilever beams were developed by curve fitting elastic finite element data from the program BASP. The equations explicitly account for the effects of bracing, load height, and moment distribution along the length of the beam. Simplified equations are proposed that are generally conservative compared to the finite element data. A design method is proposed that uses a modified factor to be used with the AISC procedure.
Errata: Multiple Bolt Anchorages: Method for Determining the Effective Projected Area of Overlapping Stress Cones
Authors: Marsh M. Lee , Burdette Edwin G.
Published: April 2024

Errata
Closure: Using Moment and Axial Interaction Equations to Account for Moment and Shear Lag Effects in Tension Members
Authors: Esptein Howard L.
Published: April 2024

Closure
Current Steel Structures Research No. 01
Authors: Bjorhovde Reidar
Published: April 2024

Current Steel Structures Research
Current Steel Structures Research No. 03
Authors: Bjorhovde Reidar
Published: April 2024

Current Steel Structures Research
Strengthening Open-Web Steel Joists
Authors: Fisher James M.
Published: April 2024

The paper presents procedures and suggested details for the strengthening of open web steel joists. Strengthening of open web steel joists is often required due to the addition of roof top units, under hung conveyors, or other loading increases not contemplated in the original specification for the joists. Three basic methods of strengthening a joist or joist system are discussed: load redistribution, adding new joists or beams, and reinforcing existing joists.
Cyclic Behavior of Single Angles for Ductile End Cross Frames
Authors: Carden Lyle P. , Garcia-Alvarez Francisco , Itani Ahmad M. , Buckle Ian G.
Published: April 2024

The cyclic inelastic behavior of single angle braces used in bridge cross frames is described in this paper. Based on the results from experiments, it is shown that steel angles can be designed to achieve a ductile response with large inelastic strains prior to failure under cyclic loading. Preventing fracture in the connections as well as satisfying limiting b/t and Kl/r ratios results in good cyclic behavior and maximum cyclic strains greater than 6%. The tensile yield force for the single angles can be confidently predicted. The buckling capacity is shown to be largely dependent on the effective length of the members which, in turn, is dependent on the type of end condition. Where plastic hinging is expected in the gusset plates an effective length factor of 1.0 can be assumed for the member, while if plastic hinging is expected in the member an effective length factor of 0.7 is appropriate, where the length is defined as the distance between the centroids of the connections. It is recommended that Kl/r for single angles in end cross frames of bridges be limited to 120 to preclude the use of slender members for which the buckling strength is sensitive to effective length. By limiting the slenderness ratio to 120, the members are treated like main members for seismic loads based on AASHTO provisions. The b/t ratio should be limited to those specified for special concentrically braced frames from the AISC Seismic Provisions for Structural Steel Buildings. An analytical model was developed to simulate the nonlinear response of the single angles and a simplified bilinear model was developed for design purposes.
Performance-Based Seismic Design of Eccentrically Braced Frames Using Target Drift and Yield Mechanism as Performance Criteria
Authors: Chao Shih-Ho , Goel Subhash C.
Published: April 2024

A new performance-based seismic design procedure for eccentrically braced frames (EBF) based on pre-selected yield mechanism and target drift is proposed in this paper. The design base shear is derived from a modified energy balance equation. A new seismic lateral force distribution based on nonlinear dynamic behavior is also presented. Two EBF (3-story and 10-story), which were used in a recent related study where they were designed by following current design practice and IBC 2000 provisions, were re-designed by the proposed performance-based design methodology by using the same basic design spectral values as used for the code designed frames. The proposed design procedure was validated by extensive non-linear dynamic analyses for a number of ground motion records. Comparisons are made between the responses of the code designed frames with the ones designed by the proposed method. The results confirm the validity of the proposed method for the study EBF in terms of meeting all the performance design objectives, such as target drifts, and intended yield mechanism, in other words, yielding occurring in a controlled manner in pre-selected elements. Thus, yielding was confined to the shear links only, and plastic hinging in the columns was eliminated except some occurring at the column bases, which was expected. This resulted in superior performance of the frames designed by the proposed method over that of the code designed frames. The total weight of steel used in the frames designed by the two approaches was the same. No attempt was made to compare the costs because of many factors that may affect them.
Progressive Collapse Analyses of 2D Steel Framed Structures with Different Connection Models
Authors: Lim Joonhong , Krauthammar Theodor
Published: April 2024

Progressive collapse is initiated by a local failure of an individual structural element that sheds additional loads on adjacent structural elements. A local failure can be defined as a loss of the load-carrying structural capacity. If any of the adjacent elements fails under the enhanced loads, additional collapses would progresses to other structural elements until a disproportionate part of the structure collapses. Therefore, it is essential to investigate the nature of progressive collapse that can result in a massive destruction of a structure. In this study, the finite element code ABAQUS/Explicit was validated and used for the analyses. 2D steel frames for various combinations of spans and stories with rigid, semi-rigid, and reinforced semi-rigid connections. This paper showed that the control of horizontal column buckling propagation is a key factor in preventing progressive collapse.
Closure: Flexible Moment Connections for Unbraced Frames Subject to Lateral Forces â€” A Return to Simplicity
Authors: Geschwindner Louis F. , Disque Robert O.
Published: April 2024

Closure
Technical Note: Determination of Allowable Strength Design Safety Factors in the 2005 AISC Specification
Authors: Duncan Cynthia J. , Fenves Steven J. , Iwankiw Nestor
Published: April 2024

The 2005 AISC Specification for Structural Steel Buildings includes both allowable stress design (ASD) and load and resistance factor design (LRFD) methods. The determination of safety factors for use in ASD are directly proportional to the resistance factors used for LRFD. The relationship between the resistance and phi factors is derived based on a live load-to-dead load ratio of 3 and the development of an equivalent load factor for LRFD. Both the resistance and phi factors are tabulated in this paper for the various limit states and structural elements that appear throughout the 2005 AISC Specification.
Impact of Recent Research Findings on Eccentrically Braced Frame Design
Authors: Richards Paul , Okazaki Taichiro , Engelhardt Michael , Uang Chia-Ming
Published: April 2024

Design provisions for eccentrically braced frames (EBFs) are based largely on results from ASTM A36 links tested at the University of California, Berkeley (UCB) in the 1980's. To address issues related to the use of ASTM A992 steel in modern EBFs, new experimental testing and finite element modeling of EBF links were performed. A total of twenty-four link specimens were tested at the University of Texas at Austin (UTA). UTA experimental data was used to validate finite element modeling techniques used in a parametric study conducted at the University of California, San Diego (UCSD). This paper highlights findings from these experimental and analytical investigations. The impact of flange width-thickness ratio, intermediate stiffener spacing, and loading protocol on link rotation capacity and failure mode are discussed. Recommendations are given for intermediate stiffener detailing that will improve link rotation capacity. Results justify the flange width-thickness requirement for EBF links in the 2005 AISC Seismic Provisions for Structural Steel Buildings, which is relaxed from the previous limit and will facilitate more economic design of EBFs. The studies also indicate that the link overstrength value adopted in the Provisions, which was originally based on A36 links, is equally valid for A992 links.
Expected Yield Stress and Tensile Strength Ratios for Determination of Expected Member Capacity in the 2005 AISC Seismic Provisions
Authors: Liu Judy , Sabelli Rafael , Brockenbrough Roger L. , Fraser Timothy P.
Published: April 2024

In the 2005 AISC Seismic Provisions for Structural Steel Buildings, a factor, Rt, has been introduced for the ratio of expected tensile strength to the specified minimum tensile strength for use in calculating a modified strength for fracture limit states within designated yielding members. Additionally, for these provisions, some revisions have been made to the expected yield stress ratios, Ry, from the 2002 AISC Seismic Provisions for Structural Steel Buildings. These changes were based on a survey of recent mill certificates, as well as a review of published tensile property surveys.