1
University Of Wasit
College Of Engineering
Department Of Civil Engineering
Block Shear
Submitted to:
Asst. Lec. Hassan Aladdin
Prepared By:
Ali Hamid Kadhim
Date of submission:
29-08-2020
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Guidelines and tips
Prepare for your exams
Study with the several resources on Docsity
Earn points to download
Earn points by helping other students or get them with a premium plan
Block shear in steel structures, Assignments of Civil Engineering
This assignment explains briefly the block shear in steel structures
Typology: Assignments
2019/2020
1 / 11
This page cannot be seen from the preview
Don't miss anything!
Related documents
Partial preview of the text
Download Block shear in steel structures and more Assignments Civil Engineering in PDF only on Docsity!
University Of Wasit
College Of Engineering
Department Of Civil Engineering
Block Shear
Submitted to:
Asst. Lec. Hassan Aladdin
Prepared By:
Ali Hamid Kadhim
Date of submission:
INTRODUCTION
1.1 Background
Tension members with bolted ends are frequently used as principal structural members in trusses and lateral bracing systems. These members are designed to resist yielding of the gross section, rupture of the minimum net section and block shear failure during the life time of the structure.
Block shear is known to be a potential failure mode which can control the load capacity of several different types of bolted connections, including shear connections at the ends of coped beams, tension member connections and gusset plates. It is a limit state that combines a tension failure on one plane and a shear failure on a perpendicular plane. Typical block shear failure mechanisms for a single angle tension member and gusset plate are shown in Figure 1.1. The ‘block’ of the connected plate bounded by the bolt holes tears out in this failure mechanism in which tensile force is developed along the upper edge of the block (tension plane) and a shear force develops along the bolt line (shear plane). P P
(a) Angle Connection (b) Gusset Plate Connection Figure 1.1 : Typical Block Shear Failure Paths
Ant , Anv , Agt , Agv are shown in Figure 1.2 below.
a) Tensile gross (b) Tensile net c) Tensile gross d) Tensile net area; shear area; shear area; shear net area; shear gross area gross area area net area
Figure1.2 : Representation of Ant , Anv , Agt , Agv
The LRFD procedure has an upper limit on the nominal strength such that its value could not exceed the value determined by considering the simultaneous fracture at the net shear and tension planes. In order to calculate the design strength, the nominal strength given by Equations 1.1 or 1.2 is multiplied by a resistance factor (φ) which is equal to 0.75.
On the other hand, in the AISC-ASD (1989) procedure, failure is assumed to occur when rupture of the net section and shear planes occur simultaneously. A factor of safety of 2 is used according to this specification. The ASD nominal load capacity without a safety factor is calculated as follows:
Rn = Fu Ant + 0.6 Fu Anv (1.3)
1.2 Previous Studies
1.2.1 Experimental Studies
1.2.1.1 Study of Ricles and Yura (1983)
Full scale testing of double-row bolted-web connections were performed on coped and uncoped ASTM grade A36 W460X89 specimens by Ricles and Yura (1983). The major variables were end and edge distances, slot length, and number of holes. 3/4- A325 (19mm) bolts and a hole diameter of 21 mm were used in the connections. The minimum edge and end distances were 25 mm. It was indicated that shear resistance is developed on the gross section rather than the net section.
1.2.1.2 Study of Hardash and Bjorhovde (1985)
Hardash and Bjorhovde (1985) tested 28 specimens to develop an improved design method for gusset plates. Gage between lines of bolts, edge distance, bolt spacing and number of bolts were considered as the strength parameters. Gusset plates fastened with two lines of bolts were tested. Test specimens had a gage length of 51, 76 and 101 mm, edge distance of 25, 38 mm, and pitch distance of 38 and 51 mm. Connections had two to five bolts in a bolt line and diameter of bolt holes were 14 and 17 mm. The average material properties of 27 specimens had a yield strength of 229 MPa and an ultimate strength of 323 MPa. One specimen had a yield strength value of 341 MPa and ultimate strength of 444 MPa. Test plates had a basic failure mode consisting of tensile failure across the last row of bolts, along with an elongation of the bolt holes. Load deformation curves of the each test specimens was obtained and it was observed that the drop in strength from the ultimate load to second strength plateau corresponded approximately to the ultimate strength of the net area at the last row of bolts. Ultimate shear resistance was more difficult to define, because, the shear stress
distances of 50.8 mm, 63.5 mm and 76.2 mm. Nine of the specimens were WT7X tension members with two, three or four bolt end connections having varying edge distances of 63.5 mm, 76.2 mm. A490 bolts in bearing, 25.4 mm in diameter and snug- tight, were used for all specimen connections. A pitch distance of 76.2 mm and an end distance of 63.5 mm were used. Experimental failure loads were compared with code treatments. Recommendations were given based on the ultimate load and the strain variation along the tension plane that was measured during the experiments.
1.2.2 Statistical Studies
1.2.2.1 Study of Cunnigham (1995)
Cunnigham (1995) performed a statistical study to assess the American block shear load capacity predictions. Even though, both ASD and LRFD equations predicts the failure loads with a reasonable level of accuracy on average, it was observed that both the ASD and LRFD block shear predictions have drawbacks in terms of anticipated failure modes. It is evident from the test results that tension and shear planes do not rupture simultaneously as assumed in ASD specification. In LRFD predictions, the equation (Equation 1.2) with shear fracture term governed, but experiments showed a failure mode similar to described in the equation (Equation 1.1) with tensile fracture term. Thus, Cunnigham set the geometric and material parameters that had been investigated and studied several other parameters such as in- plane shear eccentricity and tension eccentricity. Some equations, which include different types of failure modes and variables, were presented to predict block shear load capacity.
1.2.2.2 Study of Kulak and Grondin (2001)
Kulak and Grondin (2001) performed a statistical study on evaluation of LRFD rules for block shear capacities in bolted connections with test results. It was stated that
there were two equations to predict the block shear capacity but the one including the shear ultimate strength in combination with the tensile yield strength seemed unlikely. Examination of the test results on gusset plates reveals that there is not sufficient tensile ductility to permit shear fracture to occur.
After reviewing the test results, it was observed that failure modes seen in gusset plates and coped beams are significantly different and use of Equations 1.1 and 1. gives conservative predictions for gusset plates but they are not satisfactory for the case of coped beams. In angles block shear capacity is predicted well by these equations. As a conclusion, Kulak and Grondin (2001) recommended different equations for predicting the block shear capacities for gusset plates and coped beams to use.
1.2.3 Finite Element Studies
1.2.3.1 Study of Epstein and Chamarajanagar (1996)
Epstein and Chamarajangar (1996) studied the effects of stagger and shear lag on the failure load of angles in this study. Angles were modeled with 20 node brick elements and elastic-perfectly plastic stress strain curve for steel was used in this analysis. A strain based criterion was used to determine the failure load of the member. The nondimensionalized finite element results were compared with the full scale testing results.
1.2.3.2 Study of Kulak and Wu (1997)
Kulak and Wu (1997) observed the shear lag effect on the net section rupture of the single and double angle tension members. For practical reasons it is unusual to be able to connect the all legs of the angle and the influence of only one of the connected leg to the tensile capacity of the connection is termed as shear lag. ANSYS was used in the analysis and quadrilateral shell elements that can include plasticity
1.3. Problem Statement
Block shear failure is one of the main criteria to be considered while designing some of the steel members. American provisions for determining design load capacities for this type of failure mode first appeared in AISC-LRFD and AISCASD specifications. Over the past decades, very limited experimental and analytical researches have been conducted to predict the block shear load capacities of different types of connections. In 2004, Topkaya presented a finite element parametric study on block shear failure of steel tension members with nonstaggered holes and presented simple block shear load capacity equations. It was stated that further research was needed to determine the applicability of Topkaya’s (2004) findings to block shear failure of connections having staggered hole and multiple bolt line connections. This thesis aims to present a numerical parametric study to investigate the block shear failure load capacities of the connection geometries mentioned above. To ensure the reliability of the finite element analysis, comparison between the finite element analysis and the experimental studies will be presented for the gusset plates, angles and tee section with non-staggered bolted connections by using the methodology developed by Topkaya (2004). The quality of the current block shear capacity equations specified in the AISC-LRFD and AISC-ASD specifications and Topkaya’s research will be assessed by making comparisons with experimental findings. After ensuring the reliability of the finite element analysis predictions, new numerical investigations will be performed to identify the important parameters which influence the block shear response of multiple bolt line and staggered hole connections. If necessary, by using the obtained analytical findings new equations will be presented to predict the block shear load capacities of the aforementioned connections.
REFERENCES
American Institute of Steel Construction Inc. (AISC), Allowable Stress Design Specification for Structural Steel Buildings , 9th^ Edition, Chicago (IL): American Institute of Steel Construction, 1989.
American Institute of Steel Construction Inc. (AISC), Load and Resistance Factor
Design Specification for Structural Steel Buildings , 3rd^ Edition, Chicago (IL):
American Institute of Steel Construction, 2001.