The Role of Connection Design
Structural connections are the interfaces between members — columns to beams, beams to beams, columns to base plates, and braces to gusset plates. They are often the most complex elements to design because they must transmit combined axial, shear, and moment forces while accommodating fabrication tolerances, erection sequences, and in seismic applications, ductile inelastic behaviour.
A poorly designed connection is a structural liability even when the members themselves are correctly sized. Connection failures in steel structures are disproportionately common because they are sometimes treated as a detailing afterthought rather than a design responsibility. At Sixteens, connection design is a first-class engineering task performed with full force demand data from the structural model and explicit code verification for every limit state.
Bolted vs Welded Connections
The choice between bolted and welded connections depends on loading conditions, fabrication environment, erection sequence, and client preference. Both have distinct design requirements under AISC-360 Chapter J.
- Bolted connections — High-strength bolts (ASTM A325 / A490, or equivalent metric grades) are designed for bearing-type or slip-critical service. Slip-critical connections are required where joint movement under service load is unacceptable — critical in seismic or dynamic applications. Bolt layout, edge distances, spacing, and group eccentricity all require explicit calculation.
- Welded connections — Fillet welds and complete-joint-penetration (CJP) groove welds are sized for weld throat, effective length, and load angle. AWS D1.1 weld quality requirements and preheat provisions govern fabrication. For seismic applications, CJP welds at beam-column moment connections require enhanced toughness (CVN) requirements per AISC 341.
- Combined bolted/welded — Many practical connections use both: shop welds for speed and precision in the fabrication shop, field bolts for safe erection without hot work at height.
Types of Connections We Design
Moment Connections
Fully restrained (FR) moment connections transfer both shear and moment from beam to column. They are the primary lateral force-resisting element in moment frames. Design involves flange plate or direct weld moment transfer, web plate shear transfer, column panel zone checks (AISC-360 Section J10), and column stiffener requirements. For seismic moment frames (SMF/IMF per AISC 341), connections must meet prequalified criteria or pass testing protocols.
Shear Connections
Simple shear connections (shear tabs, single-plate connections, double-angle connections, seated connections) transfer only vertical shear. Although classified as "simple," they must still be designed for the actual shear demand with appropriate edge distances, weld sizes, and block shear checks. Eccentric shear connections require instantaneous centre of rotation analysis for bolt groups.
Gusset Plates
Gusset plates connect bracing members to beams and columns in braced frames and truss joints. Design involves the Uniform Force Method (UFM) for determining bolt and weld forces, gusset plate buckling (compression-loaded gussets), and Whitmore section tension/compression checks. In seismic applications, gussets must accommodate brace buckling deformation through a clearance zone.
Base Plates
Column base plates transfer column loads to concrete foundations through bearing, anchor rod tension, and shear friction or shear lug mechanisms. AISC Design Guide 1 procedures govern bearing area, plate thickness, and anchor rod sizing. Moment base plates require careful consideration of anchor rod placement and embedment depth for both strength and stiffness.
Seismic Connection Design
Seismic connections require a capacity design philosophy: connections must be stronger than the yielding mechanism they are designed to protect, ensuring that inelastic deformation occurs in the intended location (beam plastic hinge) rather than in the connection itself. This is particularly critical for the Antalya seismic-zone entertainment supports project, where the governing seismic demands required connections designed to AISC 341 seismic provisions with explicit ductility detailing.
Every connection is designed to the full force demand extracted from the structural model — not simplified approximations. This ensures that the connection matches the structural system's actual behaviour under design loading.
AISC-360 Compliance
AISC 360-22 Specification for Structural Steel Buildings, Chapter J covers connections in full. Key design checks we perform on every connection include: bolt shear and bearing strength, bolt slip resistance, weld effective throat and strength, block shear rupture of connected elements, net section fracture, gross section yielding, prying action in tension connections, and concentrated force checks on webs. Our design reports cite the specific equation and section number from AISC-360 for every governing check.
What Clients Receive
- Connection design calculations — Full derivation for every connection type, with governing limit states, demand/capacity ratios, and AISC-360 clause citations.
- Connection detail drawings — Dimensioned sketches or AutoCAD drawings showing bolt layout, weld sizes, plate dimensions, and material specifications.
- Bill of materials — Plate sizes, bolt grades and quantities, weld electrode classifications.
- Coordination with detailer — We provide connection forces and design requirements in a format compatible with Tekla Structures or Revit structural detailing workflows.