Connections
Structural connections transfer forces and moments between members while maintaining the intended load path of the structure. In steel construction, common connection methods include bolted and welded joints, often using gusset plates, end plates, angles, or other connection components. Connection design must consider the actual force components transferred through the joint, including tension, shear, compression, and moment. For bolted connections, important limit states include bolt shear, bolt tension, bearing on the connected material, gross-section yielding, net-section rupture, and block shear of plates. The net section is reduced by bolt holes and can govern tension rupture even when the gross area appears adequate. For welded connections, fillet weld strength is commonly based on the effective throat, while weld length, weld size, electrode strength, base-metal strength, and the direction of applied loading affect the available resistance. Connection geometry and eccentricity can produce nonuniform forces within a bolt or weld group. Bearing-type bolted connections transfer load primarily through bolt shear and bearing after contact develops, whereas slip-critical connections rely on friction generated by pretensioned bolts to limit slip under specified service loads. Connection design therefore requires checking both the fastener and the connected material rather than treating the joint as a single strength value. The governing design resistance is the lowest resistance among the applicable limit states after applying the safety format required by the governing design code. Good connection design also requires an appropriate load path, adequate edge distances and spacing, constructability, access for installation or welding, and detailing that is consistent with the assumed structural behavior.
Knowledge Check
1.What is the primary structural purpose of a connection?
2.Which of the following is a common limit state for a bolted steel connection?
3.A bolt has a nominal shear stress of 300 MPa acting over an effective shear area of 200 mm². What is the nominal shear resistance?
4.Why can bolt-hole size affect the tensile capacity of a connected plate?
5.A steel plate is 100 mm wide and 10 mm thick. If a single bolt hole of 20 mm is deducted from the critical section, what is the simplified net area?
6.What does bearing failure in a bolted connection refer to?
7.What is block shear failure?
8.In a fillet weld, what is the commonly used geometric expression for the effective throat?
9.A 6 mm equal-leg fillet weld has an effective throat of approximately 0.707w. What is the effective throat?
10.If a weld has an effective throat of 4 mm and an effective weld length of 100 mm, what is the effective weld area?
11.What is the main difference between bearing-type and slip-critical bolted connections?
12.Why is eccentric loading important when designing a bolt group?
13.A connection carries a 60 kN shear force equally through 4 identical bolts, assuming a concentric load and equal load sharing. What is the average shear force per bolt?
14.Which statement about a bolt group subjected to an eccentric shear load is correct?
15.What is the gross-section yielding limit state in a tension member connection?
16.Why can the net-section rupture check be different from the gross-section yielding check?
17.What does the effective net area A_e = U × A_n account for?
18.Which factor is especially important when checking whether a connection behaves as intended?
19.Why should bolt strength and connected-plate strength both be checked?
20.What is a major practical consideration when detailing a welded or bolted connection?