CELE Steel & Timber Design — Timber DesignConcept Map

Concept

Adjustment Factors System

Sub Concepts

• Load Duration Factor (CD): 0.9–2.0 range
• Wet Service Factor (CM): Moisture reduction
• Temperature Factor (Ct): Environmental adjustment
• Size Factor (CF): Sawn lumber scaling
• Beam Stability Factor (CL): Lateral-torsional control
• Column Stability Factor (CP): Slenderness reduction
• Repetitive Member Factor (Cr): Multiple members sharing load

Relationship To Central

Core method to convert reference design values to allowable stresses; unique to timber ASD

Concept

Bending Design (Flexural Members)

Sub Concepts

• Bending Stress Formula: fb = M/S
• Section Modulus: S = bh²/6 (rectangular)
• Allowable Bending: Fb′ = Fb × CD × CM × Ct × CF × CL × Cr
• Lateral Torsional Buckling (CL): Critical for deep beams
• Repetitive Member Factor (Cr): Multi-joist optimization
• Check Condition: fb ≤ Fb′

Relationship To Central

Primary serviceability check for beams and joists using allowable bending stress

Concept

Shear Design (Parallel to Grain)

Sub Concepts

• Shear Stress Formula: fv = 3V/(2A)
• Rectangular Section Area: A = b × h
• Allowable Shear: Fv′ = Fv × CD × CM × Ct
• Notched Support Effect: Reduced dn, amplification factor d/dn
• Common CELE Trap: Notched beams lose significant shear capacity
• Check Condition: fv ≤ Fv′

Relationship To Central

Secondary check often governing short, deep wood beams; wood weakness in horizontal shear

Concept

Compression Design (Axial Members)

Sub Concepts

• Compression Stress Formula: fc = P/A
• Allowable Compression: Fc′ = Fc* × CP
• Intermediate Value: Fc* = Fc × CD × CM × Ct × CF (no CP yet)
• Euler-like Buckling: FcE = 0.822 E′min / (le/d)²
• Column Stability Factor CP: Nonlinear reduction with slenderness
• Sawn Lumber Constant: c = 0.8 (glulam c = 0.90)
• Effective Length: le accounts for end conditions
• Check Condition: fc ≤ Fc′

Relationship To Central

Column and post design governed by slenderness via CP stability factor

Concept

Reference Design Values (Species/Grade Dependent)

Sub Concepts

• Fb: Reference bending (MPa)
• Fv: Reference shear parallel to grain (MPa)
• Fc: Reference compression parallel (MPa)
• Fc⊥: Reference compression perpendicular (MPa)
• Ft: Reference tension parallel (MPa)
• E: Modulus of elasticity (MPa)
• Emin: Minimum E for buckling calcs (MPa)
• Wood Species/Grade Tables: NSCP 2015 Chapter 6

Relationship To Central

Starting point before any adjustment factors applied; from code tables

Concept

Load Duration Factor (CD)

Sub Concepts

• Permanent Load: CD = 0.9 (10+ years)
• Normal/Ten-Year Load: CD = 1.0
• Two-Month Load: CD = 1.15 (construction season)
• Seven-Day Load: CD = 1.25 (short-term event)
• Wind/Seismic Load: CD = 1.6
• Impact Load: CD = 2.0 (mechanical shock)
• Governs Most Stress Limits: Applied to Fb, Fv, Fc, Ft

Relationship To Central

Unique to timber; rewards brief loads; key multiplier in all stress adjustments

Concept

Beam Stability & Lateral Torsional Buckling

Sub Concepts

• Lateral Restraint: Degree of bracing perpendicular to loading
• Unbraced Length: lu measured along beam axis
• Depth-to-Width Ratio: d/b affects slenderness in weak direction
• Fully Braced: CL ≈ 1.0 (decking, floor systems)
• Partially Braced: CL < 1.0 (open beams, trusses)
• CL Interaction: Competing with CF; often apply smaller governs
• Critical for Long-Span, Tall Timber Beams

Relationship To Central

CL factor prevents lateral-torsional failure of deep, slender beams under bending

Concept

Column Stability & Slenderness Effects

Sub Concepts

• Slenderness Ratio: le/d (effective length to least dimension)
• Euler Critical Stress: FcE from global buckling theory
• Stability Index: β = FcE/Fc*
• CP Formula: Quadratic solution (sawn lumber c = 0.8)
• Short Column: CP → 1.0 (crushing governs)
• Long Column: CP → 0.0 (buckling governs)
• Intermediate Range: 11 < le/d < 26 (most design range)
• Effective Length Factor K: Accounts for end conditions

Relationship To Central

CP factor (analogous to steel column buckling) reduces allowable compression in slender timber columns

Concept

Notched Beam Design

Sub Concepts

• Reduced Effective Depth: dn = d − notch depth
• Amplification Factor: (d/dn) reduces shear capacity nonlinearly
• Shear Stress at Notch: fv = (3V/2A) × (d/dn)
• Combined Tension/Shear: Interaction near notch end
• Design Rule: Avoid deep notches; limit dn/d > 0.75
• Common in Timber Trusses: Gusset plate connections often require notching

Relationship To Central

Special case of shear failure at support; classic CELE pitfall due to net section loss

Concept

NSCP 2015 & Philippine Design Standards

Sub Concepts

• Chapter 6: Wood Design (ASD method)
• Reference Standard: NDS (National Design Specification, USA) adopted with local mods
• Allowable Stress Basis: ASD philosophy for wood
• Load Combinations: Per NSCP 2010 Ch. 2 (mostly working loads)
• Material Properties: Tables for Philippine-market timber species
• Professional Practice: RA 544 (Professional Regulation Act) requires PE stamp

Relationship To Central

Regulatory framework governing all timber design in Philippine projects

Concept

Practical Applications in Philippines

Sub Concepts

• Formwork & Scaffolding: Temporary, high CD (1.25–1.6)
• Residential Floor Joists: Normal loading, CD ≈ 1.0
• Roof Trusses: Wind load, CD = 1.6; snow minimal in PH
• Bridge Decking: Waterfront structures (wet service CM < 1.0)
• Agricultural/Rural Buildings: Lower cost, timber preferred
• Connections: Bolts, nails, screws (design per NDS Chapter 11)

Relationship To Central

Common uses of timber design in Philippine construction practice

To

Adjustment Factors System

From

Allowable Stress Design ASD

Strength

strong

Relationship

ASD is the governing method; adjustment factors are the mechanism to convert reference to allowable

To

All Stress Limits Fb Fv Fc Ft

From

Load Duration Factor CD

Strength

strong

Relationship

CD is multiplied into every stress allowable; unique to wood design

To

Beam Stability Factor CL

From

Bending Design

Strength

strong

Relationship

CL controls lateral-torsional buckling of slender beams; critical for deep unrebraced members

To

Column Stability Factor CP

From

Compression Design

Strength

strong

Relationship

CP reduces allowable compression stress as slenderness ratio increases; analogous to steel column buckling

To

Notched Beam Design

From

Shear Design

Strength

strong

Relationship

Notches reduce effective depth dn and trigger amplification factor d/dn; classic CELE failure mode

To

Adjustment Factors System

From

Reference Design Values

Strength

strong

Relationship

Reference values are the starting point; all C factors are multiplied to arrive at allowable

To

Bending Design

From

Adjustment Factors System

Strength

strong

Relationship

Bending allowable Fb' is Fb times six adjustment factors CD CM Ct CF CL Cr

To

Shear Design

From

Adjustment Factors System

Strength

moderate

Relationship

Shear allowable Fv' is Fv times three adjustment factors CD CM Ct

To

Compression Design

From

Adjustment Factors System

Strength

strong

Relationship

Compression allowable Fc' is Fc* (with CD CM Ct CF) times CP (stability); two-stage process

To

Practical Applications in Philippines

From

Wet Service Factor CM

Strength

moderate

Relationship

Wet service common in PH bridge decking and waterfront structures; CM < 1.0 reduces allowables

To

Bending Design

From

Size Factor CF

Strength

moderate

Relationship

CF applies to sawn lumber; smaller sections receive higher CF; affects beam sizing economics

To

Column Stability Factor CP

From

Slenderness Ratio le/d

Strength

strong

Relationship

CP is computed from le/d via Euler critical stress and quadratic formula; governs column behavior

To

Compression Design

From

Effective Length le

Strength

strong

Relationship

Effective length accounts for end conditions; critical input to slenderness and buckling calcs

To

Allowable Stress Design ASD

From

NSCP 2015 Chapter 6

Strength

strong

Relationship

NSCP 2015 adopts NDS ASD approach for timber design in Philippines

To

NSCP 2015 Chapter 6

From

RA 544 Professional Regulation Act

Strength

strong

Relationship

PE requirement mandates compliance with NSCP; professional responsibility for timber design

To

Section Modulus S

From

Bending Stress Formula fb = M/S

Strength

strong

Relationship

Section modulus is the geometric property used to compute bending stress

To

Rectangular Section

From

Shear Stress Formula fv = 3V/2A

Strength

strong

Relationship

1.5 factor arises from parabolic shear distribution in rectangular cross-sections

To

Column Stability Factor CP

From

Compression Stress Formula fc = P/A

Strength

strong

Relationship

Allowable fc is adjusted by CP to account for buckling; check fc = P/A ≤ Fc' = Fc* × CP

To

Shear Design

From

Notched Beam Design

Strength

strong

Relationship

Notches trigger net section loss and shear stress amplification; integral to shear check

To

Load Duration Factor CD

From

Practical Applications in Philippines

Strength

moderate

Relationship

Formwork and scaffolding use high CD (1.25–1.6); residential joists use CD = 1.0