Unit
- Structural systems: Different types of structures such as frames, trusses, arches, and shells are used based on span, loading, and architectural requirements. Frames are common for buildings, trusses for bridges and roofs, arches for large spans, and shells for efficient load transfer.
- Design philosophy: Structural design follows either working stress method (allowable stress) or limit state design (strength and serviceability). Modern codes favor limit state design, which accounts for ultimate strength and deflection limits.
- Load paths: A clear load path ensures forces from roofs and floors travel through slabs, beams, columns, and foundations to the ground. Any interruption in this path can lead to failure.
- Material behavior: Steel is ductile and elastic up to high stress; concrete is strong in compression but weak in tension; timber is orthotropic. Understanding these helps select appropriate material for each element.
- Factor of safety: Codes define partial safety factors for materials and loads to account for uncertainties in material strength, loads, and analysis models. These factors ensure a margin of safety.
- Durability design: Structures must withstand environmental exposure such as corrosion, freeze-thaw, and chemical attack. Cover requirements, waterproofing, and material selection are key.
- Sustainability: Using recycled materials, optimizing sections to reduce material, and designing for deconstruction are emerging trends. Green building certifications like LEED influence design decisions.
- Standards and codes: Major codes include ASCE 7 (loads), ACI 318 (concrete), AISC 360 (steel), and IBC. Engineers must reference local codes for compliance.
- Foundation types: Shallow foundations such as spread footings and mat slabs are used when soil has adequate bearing capacity near the surface. Deep foundations including piles and drilled shafts transfer loads to stronger strata at depth when surface soils are weak or settlement must be controlled.
- Connection design: Connections between structural members must be designed to transfer moments, shear, and axial forces reliably. Welded, bolted, and riveted connections each have specific detailing requirements for strength, stiffness, and ductility to avoid brittle failure.
- Lateral load resisting systems: Braced frames, moment frames, shear walls, and core walls are used to resist wind and seismic forces. The selection depends on building height, occupancy, and seismic zone, with proper proportioning to limit drift and ensure energy dissipation.
Code Example
Python
def calculate_load_combination(dead, live, wind, snow, seismic):
# ASCE 7-16 basic load combinations
import numpy as np
combos = []
combos.append(1.4 * dead)
combos.append(1.2 * dead + 1.6 * live + 0.5 * snow)
combos.append(1.2 * dead + 1.0 * wind + 0.5 * live)
combos.append(0.9 * dead + 1.0 * wind)
combos.append(1.2 * dead + 1.0 * seismic + 0.2 * snow)
return max(combos)This Python function computes the critical design load from multiple combinations per ASCE 7. Using numpy arrays enables efficient maximum selection for design.
Quick Revision
- Structural systems include frames, trusses, arches, and shells, each suited to specific span and load conditions.
- Limit state design is the modern approach, considering both ultimate strength and serviceability.
- Load paths must be continuous and clear to safely transfer forces to the ground.
- Material selection depends on mechanical properties like ductility, compressive strength, and tensile capacity.
- Safety factors and durability provisions ensure long-term performance under uncertainties.