Inelastic Deformation and Local Slenderness Requirements for Rectangular HSS Braces

Evaluation of New Seismic provisions for special concentrically braced frames in AISC 341-22

In recent years the use of closed sections/tubes as structural members has increased significantly. Designers all around the world approve of the advantages that round as well as rectangular hollow structural sections (HSS) can offer, such as uniform strength and stiffness independent of the loading direction, high torsional and buckling strength and the aesthetic appearance. Splicing structural members is a common practice in construction to allow for long spanning trusses, changes in cross sections and transportation to site, to name but a few. The results of an experimental investigation of four bolted flange-plate connections between rectangular hollow structural sections, with bolts on all four sides, have been presented. A brief overview of different design methods for bolted flange-plate connections for square and rectangular hollow structural sections under tension load has also been given. A comparison of the load predictions of the various methods for the specimens in the experimental program supports the use of the design procedure that can be found in the AISC HSS Connections Manual (AISC, 1997).

Special concentrically braced frames (SCBFs) are economical and provide substantial lateral resistance and stiffness. They are frequently used in seismic design, since recent issues with steel moment resisting frames have increased their cost and raised doubts about their performance. Unfortunately SCBFs are not as well understood as many other structural system, because they rely on inelastic post-buckling of the brace during extreme seismic events. As a result, several research studies have been undertaken to better understand and improve SCBF seismic behavior. A research study has been in progress at the University of Washington (UW) to improve the seismic performance of SCBF gusset plate connections. To date more than 20 large-scale SCBF frames with gusset plate connections have been tested, and extensive analysis has been performed. This work is summarized, and the broad general conclusions from the experimental work are noted and demonstrated. The importance of connection stiffness and gusset plate welding and the relative performance of bolted vs. welded and tapered vs. rectangular gusset plates are shown. The results lead to recommended changes in the current design methods. In particular, a modified method for assuring end rotational capacity for brace buckling is proposed. This method provides lighter more compact gusset plates, which develop greater inelastic deformation capacity from the frame and less secondary damage to framing members.

Seismic performance of all-steel buckling-controlled braces with various cross-sections

Investigation of the seismic response of three-story special concentrically braced frames

This paper describes the experimental work on the tests of nine concrete-filled square and rectangular hollow structural section (HSS) columns subjected to axial load, uniaxial bending or biaxial bending. The experimental results suggest that the overall buckling appears accompanying with local buckling near the mid-height of column. Good agreement was found between the semi-sine wave shape and the experimental deflection shape. It is found that the cross-section remains plane before the specimen reached its load-carrying capacity. Also, the experimental results are compared with the values calculated from the AISC-LRFD, EC4 and CECS design codes, which shows that all codes provide safe bearing capacities. Compared with columns subjected to an axial load or uniaxial bending, the calculated capacities of column subjected to biaxial bending are more conservative. Among these three design codes, the capacities based on the EC4 design code yield results which are the closest to the experimental ones. The results calculated from the AISC-LRFD design code are the most conservative.

Development of centrically fused braced frame (CFBF) for seismic regions

Steel braced frames resist earthquake ground motion by undergoing several cycles of inelastic deformation. These deformations include elongation under tension and buckling in compression. To facilitate an understanding of the inelastic response of concentrically braced steel members under cyclic loading, several experimental, numerical, and analytical studies have been carried out by various researchers around the world. To overcome buckling, one of the primary failure mechanisms in Concentrically Braced Frames (CBFs), different bracing systems with recently developed mechanisms were implemented to tackle this phenomenon. The main features of these systems are to dissipate the earthquake-induced energy effectively, with minimum damage to buildings and infrastructure. Such systems still have some drawbacks, such as weight, price and specific performance issues. This work comprehensively studies CBFs, including concept, design, seismic behavior and performance for conventional, modern, and self-centering bracing systems. It summarizes 27 test programs for conventional CBFs, highlighting the different alternatives and approaches used by various researchers. Several additional studies incorporating self-centering bracing systems are also emphasized. The work finally highlights the advancements and challenges in achieving more sustainable solutions for the built environment.

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.

A longitudinal branch plate-to-rectangular hollow structural section (HSS) member connection tends to cause excessive distortion of the HSS connecting face. Such a connection therefore results in a relatively low, deformation limit state, design resistance. A "through" branch plate connection that extends through both walls of the rectangular HSS member can be used to increase the design resistance of a standard longitudinal branch plate connection. The results of an experimental test program and a corresponding numerical study, using the finite-element method on longitudinal and corresponding through branch plate-to-HSS connections are presented in this paper. The strength and behavior of longitudinal versus through branch plate-to-HSS connections is henceforth determined and a unified limit states design (LRFD) procedure for these cognate connections is proposed.

The Charpy V-notch (CVN) impact test has been widely used by operators and pipe mills to measure steel pipe resistance to fracture propagation. The tests are generally conducted at multiple temperatures to capture the transition from low impact energy nonductile regime to the high impact energy ductile regime. Due to the limitation of wall thickness and curvature of the pipe cross section, the CVN test for thin-walled line pipe generally can only be conducted with reduced size CVN coupons. The reduced size CVN coupon both decreases the measured impact energy and lowers the apparent transition temperature. Prior work (1996) developed a procedure to interpret the CVN data from various size of coupons. The procedure is also able to estimate the entire transition curve even based on a single test data point. This procedure has been widely used since then and been adopted in Section 9F.2.2 of ASME FFS-1/API 579 (2016). In this procedure, the difference between SATT from a given size CVN and the SATT of full pipe wall thickness drop weight tearing test (DWTT) was described by an equation derived from data fitting. Since the SATT of DWTT is fixed, the relationship between SATT from two different sizes of CVN coupons can be correlated through this equation. However, the wall thickness of the pipe is left in this correlation, which implies an artificial impact of pipe dimensions to the changes of SATT among CVN coupons sizes. In this paper, the equation between SATT of CVN and DWTT is updated, which both removes the pipe wall thickness from the correlation among different CVN sizes and achieves better data fitting. This update maintains all the capability of the prior procedure while improving the accuracy and clarity. Worked examples are provided at the end the paper to demonstrate the application of the updated procedure.

SummaryThe design and detailing of gusset plate connections greatly influence the seismic performance of a special concentrically braced frame (SCBF). Recently, a balanced design approach has been proposed in order to develop significant inelastic deformation from multiple yield mechanisms and to delay the failure of connections of SCBF system. Although extensive studies have been conducted on the corner gusset plate connections of SCBFs, research on the detailing of mid‐span beam gusset plates is rather limited. This study aims at investigating the required free length for the detailing of the mid‐span gusset plates with different brace slenderness ratios. A nonlinear finite element analysis has been conducted for a braced frame with 4 different values of linear clearance in the mid‐span gusset plates and 2 values of brace slenderness ratios. In all simulation models, the corner gusset plates have been designed using balanced design approach and detailed using an elliptical clearance of 8 times the gusset plate thickness. An experimental study has also been conducted on 2 gusset plate sub‐assemblages having similar brace slenderness ratio but with 2 different values of linear clearance in the middle gusset plates. The lateral drift capacity corresponding to the brace fracture and the level of damage are found to be dependent on the detailing of the gusset plates. Based on the results of numerical and experimental studies, the required free length has been recommended for the detailing of middle gusset plates of SCBFs of different brace slenderness ratios.

A unified inelastic constitutive model is proposed in which an evolution equation of the overstress is tried to be introduced to describe an isotropic strain hardening. Another significant assumption is the distinction of the inelastic deformation depending on the evolution of the overstress. Mathematical models are developed for the uniaxial cyclic inelastic deformation of 304 stainless steel and 2 1/4Cr-lMo steel at 650 °C and 550 °C, respectively. Through many numerical experiments, it is shown that the present models give good descriptions for a wide variety of cyclic loading conditions.

Concrete-filled and bare 6082-T6 aluminium alloy tubes under in-plane bending: Experiments, finite element analysis and design recommendations

One of the important variables in the design of the end cap calorimeter is the number of angular divisions that should be made in the face of the calorimeter array. While it would be ideal to have no such divisions, they are unavoidable because the maximum size for uranium sheets is less than the diameter of the array. These divisions create regions which are either partially or totally devoid of absorber and readout. It is the purpose of this note to analyze the effects of different parameters on the size of these cracks. This analysis assumes wedge shaped structures of significant depth (i.e. > 20% of the total depth). For such modules there are five variables which affect the size of a crack. They are: (1) The clearance between modules. The extent to which the module wall and the array extend into this region depends on the tolerances on the manufacture of the module. All of the module construction techniques currently under consideration have very tight tolerances (e.g. 2 mils). Therefore, this region is assumed to be void of solid material. In the C.C this region is thought to be .090 inches wide. (2) The thickness of the module walls. The wall thickness depends on which module is discussed. Design thicknesses range from .078 inches in the C.C. modules to .150 inches in the E.C leakage modules. Because tight tolerances are assumed on the construction of the modules the skin is assumed to be perfectly flat. (3) The dimension tolerance on the uranium width. The effect of the dimension tolerance varies depending on the location of the module. Modules near the a o'clock and 9 o'clock position will see a gray zone equal to the dimension tolerance at the top of each module. There will be a solid black zone at the bottom of each module. This results from gravity pulling the uranium plates down to touch the lower wall of the module. Modules near the 6 o'clock and 12 o'clock region will see a gray zone equal to the dimension tolerance at both edges of a module since there are no plans for a mechanism to insure their alignment along one wall. (4) The straightness tolerance on the plate edges. The straightness tolerance creates a gray zone equal to its width along each side of a module. (5) The region of reduced signal pickup. The extent of this region is not yet well understood. The current design requires an area along the edge of the module which does not have resistive coat. The width of this region has not been determined. Some portion of this region should still collect all of the signal. The size of this region is not known, either. As an example we can use the tolerances currently achieved for the Harvard plates at Rocky Flats. The width tolerance requested was +0.000, -0.020 inches. Rocky Flats is delivering plates with a width tolerance of +0.000, -0.040 inch. There is no tolerance on the straightness of the datum edge. If we assume that .010 inch of the .040 inch tolerance is do to straightness variation then we can determine the crack sizes for a C.C. E.M. module.