CELE Steel & Timber Design — Steel ConnectionsConcept Map

Concept

Bolted Connections

Sub Concepts

• Bolt Shear Strength
• Bearing Strength
• Slip-Critical Connections
• Bolt Tension
• Block Shear Rupture
• Double Shear vs Single Shear

Relationship To Central

Primary connection method; uses discrete fasteners to transfer force

Concept

Welded Connections

Sub Concepts

• Fillet Welds
• Groove Welds
• Weld Throat Area
• Electrode Classification
• Effective Weld Length
• Full Penetration Design

Relationship To Central

Alternative connection method; creates continuous force transfer

Concept

Limit States & Failure Modes

Sub Concepts

• Shear Rupture
• Bearing Deformation
• Tensile Rupture
• Block Shear Rupture
• Weld Throat Rupture
• Slip at Service Load

Relationship To Central

Governs design strength calculations; determines governing failure

Concept

Design Parameters

Sub Concepts

• Material Properties (Fy, Fu)
• Bolt Diameter & Area
• Plate Thickness
• Edge & Pitch Distances
• Electrode Strength (FEXX)
• Resistance Factor (phi = 0.75)

Relationship To Central

Input values required for strength calculations

Concept

LRFD Methodology

Sub Concepts

• Nominal Strength Calculation
• Resistance Factor Application
• Design Strength (phi*Rn)
• Service Load Checks
• Safety Margins

Relationship To Central

Load and Resistance Factor Design framework for connection design

Concept

Code Standards & References

Sub Concepts

• AISC 360-16 Specification
• NSCP 2015 Provisions
• ASTM A325 Bolt Standards
• Electrode Classifications
• RA 544 Building Code Requirements

Relationship To Central

Regulatory framework governing connection design in Philippines

To

Double Shear vs Single Shear

From

Bolt Shear Strength

Strength

strong

Relationship

Nominal shear strength doubles when there are two shear planes instead of one; design strength = 0.75 × Fnv × Ab × (number of shear planes)

To

Plate Thickness & Edge Distance

From

Bearing Strength

Strength

strong

Relationship

Bearing capacity is directly proportional to both plate thickness (t) and edge/pitch distance (lc); larger distances increase bearing strength up to the 2.4db limit

To

Hole Diameter Cap

From

Bearing Strength

Strength

strong

Relationship

The 2.4×db×t×Fu term caps bearing strength; even large edge distances cannot exceed this limit, controlling over-design

To

Leg Size

From

Fillet Weld Throat Area

Strength

strong

Relationship

Throat area = 0.707 × leg size (a); throat, not leg size, is used in strength calculations; common error is using leg size directly

To

Bearing Strength

From

Bolt Shear Strength

Strength

strong

Relationship

Both limit states must be checked; connection design strength is the minimum of bolt shear and bearing, whichever is smaller

To

Angle & Gusset Connections

From

Block Shear Rupture

Strength

strong

Relationship

Block shear failure is particularly critical in angles bolted on one leg and gusset plates; must always be checked for these configurations

To

LRFD Resistance Factor phi = 0.75

From

Design Strength

Strength

strong

Relationship

All connection limit states use φ = 0.75 in LRFD; design strength = φ × nominal strength; safety factor embedded in resistance factor

To

Material Properties (Fy, Fu)

From

Nominal Strength

Strength

strong

Relationship

Nominal strength calculations depend on yield (Fy) for gross-section limits and ultimate (Fu) for net-section/rupture limits

To

A325-N vs A325-X

From

Bolt Shear Strength

Strength

strong

Relationship

A325-N (threads in shear) has Fnv = 372 MPa; A325-X (threads excluded) has Fnv = 469 MPa; choice affects bolt shear capacity significantly

To

Electrode Type (E70, E80)

From

Fillet Weld Strength

Strength

strong

Relationship

Weld nominal strength proportional to electrode strength FEXX; E70 (482 MPa) is common, E80 (550 MPa) provides higher strength

To

Governing Limit State

From

Connection Design Process

Strength

strong

Relationship

All limit states must be calculated; the minimum controls connection capacity; common exam error is reporting bolt shear without checking bearing

To

Tension Path & Shear Path

From

Block Shear Rupture

Strength

strong

Relationship

Block shear combines a shear failure plane and a tension failure plane; the sum of these two rupture paths determines capacity

To

Fillet Weld Capacity

From

Weld Effective Length

Strength

strong

Relationship

Design strength proportional to effective length L; longer welds develop higher total strength; per-unit-length strength = 0.75 × 0.60 × FEXX × 0.707a

To

Friction & Clamping Force

From

Slip-Critical Connections

Strength

moderate

Relationship

Slip-critical bolts resist load via friction (μ) between clamped surfaces; required when slip cannot be tolerated (fatigue, dynamic loading)

To

Bearing & Block Shear Strength

From

Plate Thickness

Strength

strong

Relationship

Thicker plates improve both bearing strength (proportional to t) and block shear net area; minimum practical thickness often set by bearing or shear limits

To

Bolt Cross-Sectional Area

From

Bolt Diameter

Strength

strong

Relationship

Bolt shear strength proportional to Ab = π×db²/4; larger bolts significantly increase shear capacity but also affect bearing and hole dimensions

To

NSCP 2015 Adoption

From

AISC 360 Specification

Strength

strong

Relationship

NSCP 2015 in Philippines is based on AISC 360-16; formulas, resistance factors, and procedures are identical; RA 544 requires compliance

To

Bearing Strength Cap

From

Edge Distance Limit

Strength

strong

Relationship

Edge distance affects bearing strength via the 1.2×lc×t×Fu term, but is capped by 2.4×db×t×Fu; very large edge distances do not increase bearing beyond the cap

To

Net Section Area

From

Member Rupture

Strength

moderate

Relationship

Member tensile capacity at the bolt-hole section; net area = gross area minus area of holes; often checked separately from connection but must be verified

To

Full Penetration

From

Groove Weld

Strength

strong

Relationship

Full-penetration groove welds develop the full strength of the base metal; no strength reduction from weld geometry; controls member rupture at net section instead

To

Interaction with Shear

From

Bolt Tension

Strength

moderate

Relationship

When bolt carries both shear and tension, combined stress reduces capacity; interaction formula adjusts shear strength when tension is present

To

Plate Thickness

From

Minimum Weld Size

Strength

moderate

Relationship

AISC J2.2 specifies minimum fillet weld size based on plate thickness; thicker plates require larger welds; common sizes 1/4" to 1/2"

To

Bolt Hole Spacing

From

Clear Distance lc

Strength

moderate

Relationship

Clear distance is the gap between the edge of one hole and the edge of the next (or plate edge); controls bearing strength; minimum pitch typically 2.67×db

To

Governing Failure Mode

From

Design Strength Determination

Strength

strong

Relationship

Process: (1) calculate all limit states, (2) identify minimum, (3) that minimum is connection design strength; board exams heavily test this concept