Building Materials

Introduction

Building materials are the backbone of every structural system, shaping performance, cost, schedule, and sustainability from concept through operations. For structural engineers, “materials” means more than just choosing concrete, steel, timber, or masonry—it means selecting the right grade, product form, and details that deliver the intended behavior under gravity and environmental actions. The right choice creates a reliable load path, meets serviceability limits, and remains durable across the project’s exposure conditions.

This guide compares the most common structural materials, explains how to evaluate properties and durability, and shows how to tie material choices to design topics such as structural analysis, wind and seismic design, and foundation design. We also link to deeper dives on steel design, concrete design, and timber design.

Choose materials by performance—strength, stiffness, durability, fire, vibration—and by constructability, cost, and carbon across the full life cycle.

How Structural Engineers Select Materials

Material selection begins with performance objectives: spans, loads, vibration limits, drift/deflection, fire ratings, durability, schedule, and budget. Early collaboration with the architect and contractor often determines whether a project uses steel frames, reinforced concrete, engineered timber, masonry, or hybrids. Below are the biggest drivers:

Performance: Stiffness (deflection, vibration), strength, stability under wind/seismic, and robustness (redundancy/ductility).
Durability & Exposure: Corrosive environments, freeze–thaw, marine chlorides, sulfate soils, termites/decay for timber.
Fire & Thermal: Required ratings, thermal mass, insulation strategy, and detailing for fire resistance.
Constructability: Local trades and equipment, tolerances, site logistics, prefabrication potential.
Cost & Schedule: Material unit cost, labor/fabrication time, lead times, and formwork/erection complexity.
Sustainability: Embodied carbon, recycled content, bio-based options, and end-of-life reuse.

System Fit

Long spans and fast erection often suggest steel; repetitive floors with fire/thermal benefits favor concrete; low-carbon mid-rise with prefabrication may lean toward mass timber; durable shells and partitions often employ masonry.

Material Profiles: Strengths, Tradeoffs & Use Cases

No single material wins across all criteria. The best projects combine materials intelligently—steel frames with concrete cores, hybrid timber floors, or masonry shear walls with steel diaphragms. Here’s a comparative overview with links to deeper pages.

Concrete: Excellent compression strength, stiffness, and fire resistance; thermal mass benefits; requires formwork and curing. Ideal for slabs, cores, retaining structures, and foundations. Learn more in concrete design and reinforced concrete structures.
Steel: High strength-to-weight, ductile, fast erection, long spans; requires fire protection and corrosion strategy. Excellent for frames, trusses, and retrofit plates. See steel design and truss systems.
Timber: Lightweight, low embodied carbon, prefabrication-friendly; moisture and fire behavior require detailing; serviceability often governs. Great for mid-rise floors/roofs and hybrid systems. Explore timber design and sustainable structures.
Masonry: Compression strength, durability, fire resistance; useful for shear walls, partitions, and facades; consider reinforcement and movement joints. See masonry structures.
Composites & Hybrids: Steel–concrete composite floors, FRP strengthening systems, and timber–concrete composites can tune performance, weight, and vibration response.

Did you know?

Early system choice can reduce material use by double digits through smarter spans, grids, and diaphragm/lateral system pairing.

Properties, Models & Material Testing

Engineers translate material behavior into models for analysis and design. Strength, stiffness, density, toughness, and creep/shrinkage (for concrete and timber) shape both ultimate and service performance. Testing (e.g., cylinder breaks, coupon tests, moisture content) verifies assumptions and quality.

Useful Relationships (Conceptual)

\( w = \gamma V,\quad \sigma = \dfrac{F}{A},\quad \Delta = \dfrac{F L}{A E},\quad E_{\text{eff}} \xrightarrow[]{\text{cracking/creep}} \text{reduced} \)

\( \gamma \)Unit weight (material density × g)

\( E \)Elastic modulus (stiffness)

\( \Delta \)Axial deformation

Concrete: \( f’_c \) at 28 days, modulus from mixture and aggregates, time-dependent creep/shrinkage; rebar yield \( f_y \) and development length control ductility and anchorage.
Steel: Yield \( F_y \), tensile strength \( F_u \), toughness (CVN), weldability; section class controls local buckling and plastic capacity.
Timber: Species/grade values for bending \( F_b \), tension \( F_t \), compression \( F_c \), shear \( F_v \), and modulus \( E \); adjustments for moisture, duration of load, size, temperature.
Masonry: Prism strength \( f_m \) with reinforcement and grout effects; mortar type influences bond and durability.

Important

Model diaphragm stiffness and connection rigidity consistently with material behavior—assumed fixity or cracking can swing drift and force distribution significantly.

Durability & Exposure Conditions

Structures live outdoors. Moisture, chlorides, carbonation, freeze–thaw, UV, and biological attack degrade materials over time. Durability starts with material choice and continues with details that keep assemblies dry and maintain protective layers.

Concrete: Use appropriate cover, low water–cement ratio, air entrainment for freeze–thaw, and SCMs (fly ash, slag, silica fume) to reduce permeability; protect against chlorides and sulfates.
Steel: Specify coatings (galvanizing, metallizing, paint systems), detail to avoid water traps, manage crevices for slip-critical faying surfaces, and plan maintenance intervals.
Timber: Keep it dry—provide overhangs, flashings, ventilation gaps, capillary breaks, and decay-resistant species or treatments where necessary.
Masonry: Control cracking and moisture with movement joints, flashing, weeps, and appropriate mortar; protect ferrous anchors from corrosion.

Inspection Matters

Pair good detailing with scheduled structural inspections to catch early deterioration and preserve capacity.

Fire Performance, Thermal Mass & Envelope Interface

Fire ratings protect life and property by delaying structural failure and limiting heat transmission. Materials respond differently: steel loses strength and stiffness as temperature rises; concrete spalls and loses cover; timber chars, forming a protective layer that slows heat penetration. Thermal mass in concrete moderates temperature swings; timber/steel need complementary envelope strategies.

Concepts

\( t_\text{residual} = t_0 – \beta_0 t_f \quad\text{(timber char)}\quad;\quad q \propto V^2 \ \text{(wind);}\ \ \alpha = \dfrac{k}{\rho c_p} \ \text{(thermal diffusivity)} \)

\( \beta_0 \)Effective char rate

\( \alpha \)Thermal response parameter

Coordinate fire protection with system choice: spray-applied protection or intumescent coatings for steel; cover and spalling mitigation for concrete; char design and encapsulation for timber; fire-resistive masonry assemblies for walls and shafts.

Sustainability & Embodied Carbon

Material decisions strongly influence embodied carbon. Strategies include efficient spans and grids, composite action, optimization of member sizes, cement replacement in concrete, high-recycled-content steel, and responsibly sourced timber. Think whole-life: manufacturing, transport, construction, use, maintenance, and end-of-life reuse or recycling.

Practical Levers

Right-size member depths, select realistic strength grades, reduce over-specification, and coordinate openings/MEP to avoid rework. Hybrid systems often balance carbon, cost, and performance.

Cost, Schedule & Constructability

Materials affect both direct costs and indirect schedule impacts. Steel shines with prefabrication and fast erection; concrete offers local supply and integrated fire resistance but requires formwork and curing; timber enables off-site fabrication and lighter foundations but demands moisture-safe sequencing. Engage fabricators and contractors early to rationalize sizes, standardize details, and select connection types that field crews can execute reliably.

Standardization: Limit section sizes and rebar bar marks; repeat connection details.
Tolerances: Choose details that absorb erection tolerances without inducing stress concentrations.
Logistics: Consider site access, crane picks, pour breaks, and panel sizes for mass timber and precast.

Codes, Standards & Trusted References

Material selection and design are governed by building codes and consensus standards. While local adoption varies, the following homepages are stable entry points to authoritative content and updates:

ICC: International Building Code and adoption resources. Visit iccsafe.org.
ASCE: Minimum design loads and hazard criteria. Visit asce.org.
AISC: Steel specifications and manuals. Visit aisc.org.
ACI: Concrete building code and practice guides. Visit concrete.org.
AWC: Timber standards and design tools. Visit awc.org.
ASTM International: Material specifications and test methods. Visit astm.org.
NIST: Research and building science resources. Visit nist.gov.

For system context, explore related pages on steel design, concrete design, timber design, and masonry structures.

Procurement, Submittals & QA/QC

The best specifications fail without disciplined procurement and quality control. Material certificates, mill test reports, mix designs, shop drawings, and inspection/testing plans connect design intent to what gets built. Coordinate submittals with realistic lead times and field verification.

Concrete: Approve mix designs (strength, slump, SCMs, air), verify placement/curing plans, and schedule test cylinders.
Steel: Mill certs for grades, welding procedures (WPS/PQR), bolt certificates, and galvanizing/paint specs.
Timber: Species/grade documentation, moisture targets, fabrication drawings for glulam/CLT, and fastener data.
Masonry: Prism testing program, mortar/grout submittals, and reinforcement/anchor layouts.
Inspections: Engage special inspections for high-risk items—post-installed anchors, welds, high-strength bolts, and hold-down systems.

Common Pitfalls

Unvetted substitutions, missing corrosion protection details, and disconnects between analysis assumptions (rigid diaphragm, fixed base) and actual details (semi-rigid, foundation springs) can erode safety margins and serviceability.

Frequently Asked Questions

Which building material is “best” for structural frames?

There is no universal best—choose based on span, height, exposure, schedule, trades, and sustainability goals. Many projects are hybrids: steel frames with concrete cores, or timber floors on steel beams.

How does material choice affect seismic design?

Material ductility and detailing rules drive the response modification factor and drift capacity. Concrete and steel can deliver high ductility with the right detailing; timber shear walls rely on connection behavior. See seismic design.

What typically controls—strength or serviceability?

For long spans and lightweight systems, serviceability (deflection, vibration, drift) often governs depth and connection stiffness. Heavy systems may be governed by strength and foundation capacity.

Can low-carbon choices raise cost?

Not necessarily. Early optimization, realistic strengths, and hybrid systems often reduce both carbon and cost by using less material and speeding erection.

Key Takeaways & Next Steps

Building materials shape the entire project: behavior, durability, fire safety, schedule, and carbon. Start by defining performance goals and exposure, then select systems and details that deliver a reliable load path from roof to foundations. Model stiffness and connections realistically, plan for inspections, and coordinate with the envelope to keep assemblies dry. For deeper dives, continue to steel design, concrete design, and timber design, and explore masonry structures for walls and partitions.

For authoritative references and the latest standards, begin at ICC, ASCE, AISC, ACI, AWC, ASTM, and NIST. The right material—well detailed and well built—turns design intent into safe, resilient, and sustainable structures.