Steel Tension Members - Concept Map
Steel Tension Members: Design & Analysis for Truss Ties, Bracing, Hangers & Sag Rods
Related concepts
Tensile Strength Limit States
Sub concepts
- Tensile Yielding on Gross Section (Ductile)
- Tensile Rupture on Net Section (Sudden)
- Design Strength Comparison & Controlling Limit State
Relationship to central
Core design checks that govern member capacity; two competing failure modes must both be verified
Net Area Computation
Sub concepts
- Gross Area & Hole Diameter Allowance
- Simple Net Area (Straight Path)
- Staggered Holes & Zig-Zag Paths
- Effective Net Area & Shear-Lag Factor
- Shear-Lag Coefficient U
Relationship to central
Essential for rupture limit state; accounts for bolt-hole reductions and staggered-hole geometry
Strength Calculation Framework (LRFD)
Sub concepts
- Resistance Factors (phi) by Limit State
- Nominal Strength Formulas
- Design Strength vs. Factored Demand
- Comparison of Yield vs. Rupture Capacities
Relationship to central
Load and resistance factor design methodology; governs design practice in NSCP 2015 / AISC 360
Member Geometry & Connections
Sub concepts
- Bolt Hole Spacing & Patterns
- Connection Type & Load Transmission
- Cross-Sectional Elements & Attachment
- Pitch, Gage & Stagger Definitions
Relationship to central
Physical details that determine net area, shear lag, and effective strength
Slenderness & Serviceability
Sub concepts
- Slenderness Ratio L/r ≤ 300
- Least Radius of Gyration
- Tension Member Buckling (Not a Design Limit)
- Practical Application & Code Compliance
Relationship to central
Recommended limits to control sag, vibration, and aesthetic concerns (non-mandatory for tension)
Block Shear & Connection Failures
Sub concepts
- Block Shear Definition & Mechanics
- Shear & Tensile Rupture Paths
- Design for Block Shear Capacity
- Connection Adequacy Check
Relationship to central
Additional rupture mode at the connection zone; critical for bolted end connections
NSCP 2015 & AISC 360 Code Requirements
Sub concepts
- LRFD Method & Load Factors
- Material Properties (Fy, Fu)
- Resistance Factor Definitions
- Code Compliance & Verification
Relationship to central
Regulatory framework and design standards applicable in the Philippines and internationally
Design & Sizing Procedures
Sub concepts
- Member Selection by Trial & Iteration
- Verification of Both Limit States
- Effective Area Adjustments
- Final Capacity Confirmation
Relationship to central
Step-by-step methodology to select adequate tension members for prescribed loads
Concept connections
- Tensile Yielding on Gross SectionTensile Rupture on Net SectionBoth are mandatory limit states; the lower design strength (φPn) governs the member's capacity and controls sizing
- Gross Area AgTensile Yielding on Gross SectionGross area is the input parameter for the yield limit state; full cross-section assumed active
- Net Area AnTensile Rupture on Net SectionNet area (reduced by bolt holes) is the input parameter for the rupture limit state; failure occurs at holes
- Staggered Holes & Zig-Zag PathsNet Area ComputationStaggered arrangement requires checking multiple failure paths and using the s²/4g recovery term for diagonal segments
- Shear-Lag Factor UEffective Net Area AeU is multiplied by An to get Ae; accounts for non-uniform stress distribution in partially connected members
- Member Geometry & ConnectionsShear-Lag Factor UConnection type (all elements vs. one leg bolted) directly determines U value; geometry dictates load transmission
- Resistance Factor 0.90 (Yield)Tensile Yielding on Gross Sectionφ = 0.90 is applied to the nominal yield strength Pn = Fy × Ag to get design strength
- Resistance Factor 0.75 (Rupture)Tensile Rupture on Net Sectionφ = 0.75 (lower than yield) is applied to the nominal rupture strength Pn = Fu × Ae to account for higher variability
- NSCP 2015 & AISC 360 Code RequirementsResistance Factors (phi)Code specifies the φ values (0.90 for yield, 0.75 for rupture) to achieve consistent reliability margins
- Design Strength Comparison & Controlling Limit StateMember SizingThe lower of the two design strengths determines what section size is required; the controlling mode drives selection
- Slenderness Ratio L/r ≤ 300Tension Member Buckling (Not a Design Limit)Slenderness is recommended but not mandatory for tension; no buckling failure occurs, but limits sag and vibration
- Bolt Hole Spacing & PatternsNet Area ComputationSpacing parameters (pitch, gage, stagger) define the bolt pattern and determine which failure path is most critical
- Pitch, Gage & Stagger DefinitionsStaggered Holes & Zig-Zag PathsPitch (s) and gage (g) are the geometric inputs required to calculate the s²/4g recovery term for staggered holes
- Load Transmission PathShear-Lag Coefficient UHow force flows through the member and connection determines whether shear lag occurs; full connection → U=1.0, partial → U<1.0
- Block Shear & Connection FailuresTensile Rupture on Net SectionBlock shear is an additional rupture mode at the connection zone; both tensile rupture (net area) and block shear must be checked
- Material Properties (Fy, Fu)Limit States & StrengthFy (yield stress) and Fu (ultimate stress) are the input material parameters for both yield and rupture calculations
- Design ProcessMember Sizing by Trial & IterationSystematic procedure: select trial section → check yield → check rupture → verify slenderness → adjust if needed
- Verification of Both Limit StatesDesign & Sizing ProceduresDesign methodology requires checking both yield and rupture; both must be satisfied before design is complete
- Hole Diameter dh and Clearance AllowanceNet Area ComputationHole diameter includes bolt diameter plus clearance (typically 2–3 mm); directly subtracted from gross width to get net width
- LRFD Method & Load FactorsDesign Strength vs. Factored DemandLRFD requires φ·Pn ≥ Pu (factored load); resistance factors and nominal strengths apply this safety format
Diagrams
Steel Tension Members – Full Concept Hierarchy
Comprehensive mind map showing all major concepts in steel tension member design: limit states (yielding vs rupture), net area computation with staggered holes, connection details, code requirements, and design verification steps. This is the primary conceptual organizer for the chapter.
Tension Member Design Verification Flowchart
Step-by-step flowchart for designing a tension member in LRFD: trial member selection, gross-area yield check, net-area rupture check (with staggered-hole adjustment and shear-lag factor), determination of controlling limit state, and slenderness verification. This guides the engineer through the complete design process.
Net Area Computation for Staggered Holes
Detailed flowchart for computing net area when bolt holes are staggered: distinguishes straight vs. zig-zag failure paths, explains the s²/4g recovery term for each diagonal segment, and shows how to find the controlling (minimum) net area. Essential for complex hole patterns common in practice.
Yield vs. Rupture – Controlling Limit State Decision
Decision logic for identifying which limit state governs: compares yield (high ϕ, low stress, full area) against rupture (low ϕ, high stress, reduced area). Shows why neither can be ignored and how the lower design strength controls design. Guides the engineer to select the correct basis for member sizing.
Shear-Lag Factor U – Connection Type Classification
Classification flowchart for determining the shear-lag factor U based on connection type: full connections (U=1.0) vs. partial connections (U<1.0). Explains how load does not transmit uniformly through unconnected elements, reducing effective net area. Critical for accurate rupture-strength calculations.
Relative Contribution of Limit States in Practice
Distribution of which limit state typically controls in real tension member design projects: rupture at bolt holes dominates because the stress concentration and reduced area often overwhelm the higher yield stress advantage. Emphasizes importance of careful net-area and hole-spacing design.