ARCHE 4: Steel and Timber Design - Theory & Concepts

ARCHE 4: Steel and Timber Design

$Learning Objectives$

Navigate the National Structural Code of the Philippines provisions governing structural steel and wood design.
Relate structural behavior and load paths to member selection, stability, serviceability, connection detailing, and architectural form.
Apply the appropriate ASD or LRFD design workflow without mixing incompatible provisions or editions.
Design and review timber and steel members using explicit strength, stability, serviceability, and detailing limit states.
Communicate structural decisions through code references, calculations, sketches, and constructible architectural details.

$Governing Code Basis$

This course is governed by NSCP C101-15, Volume I, Seventh Edition (2015). Structural steel design is organized around Chapter 5 — Structural Steel, while timber design is organized around Chapter 6 — Wood. Chapter 2 is used when the lesson requires load combinations or load effects.

International source standards such as AISC and the NDS are valuable for commentary, background, and interpretation, but they do not replace the governing NSCP basis. When a newer international provision differs from the adopted NSCP provision, the lesson must identify that distinction explicitly rather than silently mixing editions.

$Code Map for ARCH 4$

Timber: Chapter 6 covers general requirements, durability, wall/floor framing, sheathing, diaphragms and shear walls, design values, member design, sawn lumber, glulam, and timber fasteners. The principal member-design provisions used in this course are Sections 615–619.

Steel: Chapter 5 organizes member design by limit state: tension (Section 504), compression (Section 505), flexure (Section 506), shear (Section 507), combined forces (Section 508), connections (Sections 510–511), serviceability (Section 512), and fabrication/erection/quality control (Section 513).

Students should learn to cite the governing section as part of every complete design solution.

$How to Use Numerical Values in ARCH 4$

Every number used in a design calculation must have a visible source category:

Source category	Examples	Acceptable use
Governing NSCP table/equation	resistance factors, member limits, connection geometry	Final code-based course calculation
Recognized product/shape data	steel section properties, engineered-wood report values	Use only for the identified product/section
Problem-supplied data	$F_y$ , $F_b$ , $E$ , dimensions, rounded mechanics inputs	Use only for the stated worked problem; never imply it is an NSCP value

When a lesson provides problem-supplied data, it must say so. When a calculation requires a lookup from a licensed or product-specific table, the lesson should identify what must be looked up and why, rather than inventing a generic value.

$Unit-System Discipline$

ARCH 4 uses SI units as the default learner-facing convention. Some steel equations and legacy shape-property examples originate in U.S. customary units; when those are used, keep the entire calculation in one unit system or convert every input before substitution. Never mix ksi/in/ft values with MPa/mm values inside one equation.

$Edition Discipline$

Do not combine design values, resistance factors, safety factors, equations, or detailing limits from different code editions unless the comparison is explicitly identified as supplemental. A calculation is not review-ready until its governing NSCP edition and design method are clear.

$Structural Design as a Load-Path Problem$

A building is not a collection of isolated beams and columns. Gravity and lateral actions must travel through a continuous load path:

surface loads → secondary framing → primary framing → columns/walls/braces → connections → foundations → ground.

For architecture students, this load-path view is essential because grids, openings, atria, façade systems, floor depth, ceiling zones, exposed structure, and lateral-system placement all affect structural feasibility.

$Explore the Gravity Load Path$

Change the tributary width while holding span and surface load fixed. Doubling the width doubles the beam line load and both support reactions. Then double the span: the reactions double again, but the maximum bending moment increases fourfold. Trace each reaction through its connection to a column and foundation; equilibrium alone does not establish their capacities.

Controls

6.0 m

3.0 m

4.0 kPa

Tributary area18.0 m²

Beam line load12.0 kN/m

Total gravity load72.0 kN

Each support reaction36.0 kN

Maximum beam moment54.0 kN·m

Equilibrium: two reactions total 72.0 kN, equal to the applied load.

Gravity analysis only. Connections transfer these reactions onward to columns and foundations. This model does not establish member capacity or include adjacent bays, continuity, lateral loads, load combinations, or foundation resistance. Arrow lengths are symbolic.

Tributary Strip Equilibrium

Service-load analysis of a simply supported beam carrying a uniform tributary floor strip; this is independent of the later material-strength check.

w=qs,\qquad R_A=R_B=\frac{wL}{2},\qquad M_{\max}=\frac{wL^2}{8}

Variables

Symbol	Description	Unit
$q$	Uniform surface load, including any self-weight being considered.	kPa
$s$	Tributary floor width assigned to the beam.	m
$L$	Simply supported beam span.	m
$w$	Uniform beam line load.	kN/m
$R_A,R_B$	Upward support reactions.	kN
$M_{\max}$	Sagging moment at midspan.	kN·m

$Strength, Stability, Serviceability, and Detailing$

A review-ready design checks more than nominal strength.

Strength: yielding, rupture, shear, bearing, block shear, fastener/weld resistance, and other material limit states.
Stability: member buckling, lateral-torsional buckling, local element slenderness, column stability, and system bracing.
Serviceability: deflection, vibration, slip, movement, moisture effects, and other performance limits.
Detailing: edge distances, spacing, bearing lengths, bracing points, connection geometry, fabrication clearances, durability, and fire/protection requirements.

The governing condition is the check with the least available reserve, not simply the first equation evaluated.

$Design Workflow Map$

Follow the complete structural-design loop below. A failed strength, stability, serviceability, detailing, durability, or constructability check sends the design back for revision rather than being documented as acceptable.

ARCH 4 Structural Design Workflow

NSCP-first design sequence from system definition through documented acceptance.

$Material-Specific Design Logic$

The general structural-design loop branches into two different material workflows:

Timber

Reference product and grade → reference design property → property-specific environmental/product adjustments → calculated stability adjustment where required → final adjusted design value → member/connection check.

Do not skip directly from a species name to $F'$ .

Steel

Material specification + section properties → classify the relevant plate elements → select the member/connection limit-state case → calculate nominal resistance $R_n$ → apply the selected LRFD or ASD factor → check stability, serviceability, and force transfer.

Do not skip directly from a section designation to a single "capacity."

The detailed workflows in Modules 1–9 are part of the design method, not optional illustrations.

$ASD and LRFD$

Timber design in this course primarily follows the NSCP wood provisions and adjusted reference design values. Steel design may use LRFD or ASD when permitted by the governing NSCP provisions, but one problem must use a consistent design basis from demand through available strength.

For steel, LRFD compares required strength from the applicable LRFD load combinations with design strength, while ASD compares required strength from the applicable ASD load combinations with allowable strength. ASD combinations are not generically synonymous with an arbitrary "service-level" load case. Never combine LRFD load effects with ASD safety factors or vice versa.

General Strength Check

Generic form used to organize a design check; the actual resistance and factors come from the applicable NSCP section.

\text{Required effect} \le \text{Available resistance}

Variables

Symbol	Description	Unit
$R_u$	Required factored strength or load effect when using LRFD.	-
$\phi R_n$	LRFD design strength.	-
$R_a$	Required strength or load effect from the applicable ASD load combination.	-
$R_n/\Omega$	ASD allowable strength.	-

$Architectural Decision Framework$

For every design problem, ask four additional questions:

Space: How does member depth or width affect clear height, planning, façade, and MEP coordination?
Expression: Is the structure exposed, concealed, or part of the architectural language?
Constructability: Can the connection actually be fabricated, erected, tightened, welded, inspected, and maintained?
Durability and fire: What exposure, moisture, corrosion, termite, fire, or protection requirements change the material/detail?

A structurally adequate member can still be a poor architectural solution if these questions are ignored.

$Course Sequence$

Part I — Timber

Module 1: material behavior, grading, design values, adjustment factors, durability, and engineered wood.
Module 2: timber tension and compression members.
Module 3: timber beams, stability, shear, bearing, and deflection.
Module 4: combined stresses, fasteners, connections, diaphragms, shear walls, and timber system detailing.

Part II — Steel

Module 5: material behavior, shapes, design philosophy, section behavior, and stability concepts.
Module 6: tension members and their connections.
Module 7: compression members and buckling.
Module 8: flexural members, shear, serviceability, and beam-columns.
Module 9: bolted/welded connections, base plates, anchors, HSS connection awareness, and fabrication/detailing.

Key Takeaways

ARCH 4 is explicitly based on NSCP C101-15, Volume I, Seventh Edition (2015).
A complete solution identifies the governing NSCP section, design method, limit state, assumptions, units, and conclusion.
Structural design must address strength, stability, serviceability, detailing, durability, fire/protection, and constructability.
Architecture and structural engineering meet at the load path: grids, openings, spans, member depth, lateral systems, and connections must be coordinated from the beginning.
Newer AISC/AWC/NDS material may be used for context only when it is clearly separated from the governing NSCP basis.

$References$

Association of Structural Engineers of the Philippines (ASEP) — National Structural Code of the Philippines, C101-15, Volume I, Seventh Edition (2015) — Governing ARCH 4 course basis for timber and structural steel design; consult the official licensed code for complete provisions, tables, equations, exceptions, and detailing requirements.

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