Study guide
7.1 Loads (Dead, Live, Construction, Wind, and Preloading)
NCEES PE Civil Construction Study Guide Exam
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1 Chapter 1: Soil Mechanics
1.1 Lateral Earth Pressure 1.2 Soil Consolidation and Settlement 1.3 Effective and Total Stresses 1.4 Bearing Capacity 1.5 Slope Stability
2 Chapter 2: Site Layout and Development
2.1 Layout and Control 2.2 Horizontal and Vertical Curves 2.3 Site Investigations and Utilities
3 Chapter 3: Material Properties
3.1 Soils, Rock, and Aggregates 3.2 Concrete Material Properties 3.3 Steel Material Properties 3.4 Wood Material Properties
4 Chapter 4: Estimating Quantities and Costs
4.1 Quantity Take-Off Methods 4.2 Cost Estimating 4.3 Engineering Economics 4.4 Work Measurement and Productivity (Earned Value)
5 Chapter 5: Project Planning and Scheduling
5.1 Construction Sequencing 5.2 Activity Time Analysis 5.3 Critical Path Method and Network Analysis 5.4 Resource Scheduling and Leveling 5.5 Time–Cost Trade-Off and Crashing
6 Chapter 6: Material Production, Execution, and Quality Control
6.1 Specification Conformance and Hold-Points 6.2 Field Testing: Concrete, Soils, and Aggregates 6.3 Compaction: Principles, Calculations, and Equipment 6.4 Concrete Placement, Consolidation, and Finishing 6.5 Bolting and Welding: Structural Steel Connections 6.6 Acceptance Sampling and Statistical Quality Control
7 Chapter 7: Structural Mechanics
7.1 Loads (Dead, Live, Construction, Wind, and Preloading) 7.2 Statics and Stresses (Bending, Shear, Deflection) 7.3 Beams, Columns, and Slabs 7.4 Foundation and Retaining Wall Mechanics
8 Chapter 8: Hydraulics and Hydrology
8.1 Stormwater Collection and Drainage (Open-Channel Flow) 8.2 Runoff Analysis 8.3 Detention and Retention Ponds
9 Chapter 9: Operations and Methods
9.1 Lifting and Rigging 9.2 Crane Capacity and Stability 9.3 Dewatering and Pumping 9.4 Equipment Selection and Production Rates 9.5 Deep Foundation Installation 9.6 Excavation and Embankment (Cut and Fill)
10 Chapter 10: Support of Construction Loads
10.1 Formwork Design 10.2 Falsework and Scaffolding 10.3 Shoring and Reshoring 10.4 Bracing and Anchorage 10.5 Support of Excavation (Trenching, Cofferdams) 10.6 Erection and Equipment Loads on Permanent Structures
11 Chapter 11: Health and Safety
11.1 OSHA Construction Regulations and Safety Management 11.2 Work Zone and Public Safety (Traffic Control)
7.1 Loads (Dead, Live, Construction, Wind, and Preloading)
Key Takeaways Explain This Topic AI
Dead loads represent the fixed, permanent weight of the structure and attached materials, calculated using material densities and volumes.
Live loads account for transient forces such as occupants, furniture, and environmental factors, with specific reductions allowable under ASCE 7.
Construction loads encompass materials, crew, equipment, and impact forces, often governing the design of temporary structures like formwork and scaffolding.
Wind loads are determined based on basic wind speed, exposure category, and building aerodynamics, using formulas like the velocity pressure equation.
Load combinations, whether LRFD or ASD, ensure structural safety by accounting for the statistical probability of various loads occurring simultaneously.
Last updated: July 2026
Loads in Structural Mechanics
Understanding the various loads that a structure must withstand is the fundamental starting point for any structural analysis and design task on the PE Construction exam. Engineers must not only calculate the magnitude of these forces but also understand their nature, duration, and how they combine under different scenarios. In construction engineering, temporary loads during the building phase often exceed the permanent loads the structure will see during its operational life. This section details dead loads, live loads, construction-specific loads, wind loads, preloading, and the load combinations used to evaluate structural safety.
Why This Topic Matters for the PE Construction Exam
For the PE Construction exam, structural mechanics is not just about the final building; it heavily emphasizes the temporary conditions that exist during construction. When a concrete slab is poured, the wet concrete, formwork, workers, and buggies create a load combination that the supporting shores must carry. The exam will test your ability to correctly identify which loads apply to a given situation, calculate their magnitudes using standard unit weights and formulas, and apply the correct load factors. A firm grasp of these concepts is essential for designing safe formwork, scaffolding, bracing, and falsework, as well as understanding the behavior of the permanent structure.
Dead Loads (D)
Dead loads consist of the weight of all materials of construction incorporated into the building, including but not limited to walls, floors, roofs, ceilings, stairways, built-in partitions, finishes, cladding, and other similarly incorporated architectural and structural items, and fixed service equipment. They are permanent and stationary.
Calculation of Dead Loads
Dead loads are calculated by multiplying the volume of a component by the unit weight (density) of its material.
Common Unit Weights:
- Normal weight reinforced concrete: 150 pcf (pounds per cubic foot)
- Structural steel: 490 pcf
- Water: 62.4 pcf
- Timber (varies by species): typically 35 to 50 pcf
Example: A 6-inch thick reinforced concrete slab carries a dead load. The load per square foot is calculated as: (6 inches / 12 inches/ft) × 150 pcf = 75 psf (pounds per square foot).
Live Loads (L)
Live loads are those loads produced by the use and occupancy of the building or other structure and do not include construction or environmental loads such as wind load, snow load, rain load, earthquake load, or flood load. They are transient and can move around or change in magnitude.
Minimum Uniformly Distributed Live Loads
Codes like ASCE 7 specify minimum live loads depending on the occupancy. For example:
- Office buildings: 50 psf
- Assembly areas: 100 psf
- Heavy manufacturing: 250 psf
- Live Load Reduction
Because it is statistically unlikely that a large floor area will be fully loaded with its maximum design live load simultaneously, codes allow for a reduction in the design live load for members supporting large areas (e.g., columns, girders). The ASCE 7 formula for live load reduction is: L = L 0 ( 0.25 + 15 K L L A T ) L = L_0 \left( 0.25 + \frac{15}{\sqrt{K_{LL} A_T}} \right) L = L 0 ( 0.25 + K LL A T 15 )
Where L 0 L_0 L 0 is the unreduced live load, K L L K_{LL} K LL is the live load element factor, and A T A_T A T is the tributary area.
Construction Loads
Construction loads are a unique category of live loads that occur only during the building phase. They are critical for the design of temporary structures.
Components of Construction Loads
Material Loads: The weight of materials stored on the structure before installation (e.g., stacks of drywall, bundles of rebar).
Personnel and Equipment: The weight of the crew and the machinery they use. For example, a concrete pump truck, motorized buggies, or scissor lifts.
Impact Loads: Dynamic forces generated by moving equipment or dropping materials. Codes typically require that the static weight of equipment be multiplied by an impact factor (often 1.25 to 1.5) to account for these dynamic effects.
Formwork Pressures: When pouring concrete, the wet concrete exerts hydrostatic pressure on the vertical forms. This lateral pressure depends on the pour rate, temperature, and concrete chemistry.
Wind Loads (W)
Wind forces act dynamically on a structure but are typically simplified into equivalent static pressures for design. The magnitude of wind pressure depends on several factors.
Velocity Pressure Equation
The fundamental equation for velocity pressure, q z q_z q z , evaluated at height z z z is given by ASCE 7: q z = 0.00256 K z K z t K d V 2 (in psf) q_z = 0.00256 K_z K_{zt} K_d V^2 \text{ (in psf)} q z = 0.00256 K z K z t K d V 2 (in psf)
Where:
V V V is the basic wind speed (mph) based on historical weather data for the region.
K z K_z K z is the velocity pressure exposure coefficient, which increases with height.
K z t K_{zt} K z t is the topographic factor, accounting for wind speed-up over hills or escarpments.
K d K_d K d is the wind directionality factor.
Once the velocity pressure is found, it is multiplied by gust effect factors and pressure coefficients to determine the actual design wind pressures acting on various surfaces of the building.
Preloading and Staging Analysis
Preloading refers to the deliberate application of load to a structure or the ground prior to the final service conditions.
Soil Preloading: In geotechnical engineering, a temporary surcharge load (like a massive pile of soil) is placed over a site to accelerate consolidation settlement before the actual structure is built. Once the settlement has occurred, the surcharge is removed.
Structural Staging: Complex structures, like segmental bridges, undergo significant stress changes during different stages of construction. A staging analysis tracks the internal forces as parts of the structure are built, shores are removed, or post-tensioning is applied. The structure might experience its most critical stress state during an intermediate construction stage rather than in its final configuration.
Load Combinations
Structures must be designed to withstand various loads acting simultaneously. However, the probability of the absolute maximum of every load type occurring at the exact same moment is extremely low. Therefore, codes prescribe specific load combinations.
Allowable Stress Design (ASD) vs. Load and Resistance Factor Design (LRFD)
ASD (Allowable Stress Design): Focuses on keeping the stresses in the structure below a certain allowable limit (yield stress divided by a safety factor) under actual (service) loads. Example combination: D + L + W D + L + W D + L + W .
LRFD (Load and Resistance Factor Design): Applies load factors to the loads (usually > 1.0 >1.0 > 1.0 to account for overload) and resistance factors to the material strength (usually < 1.0 <1.0 < 1.0 to account for material variation). Example combination: 1.2 D + 1.6 L + 0.5 ( L r or S or R ) 1.2D + 1.6L + 0.5(L_r \text{ or } S \text{ or } R) 1.2 D + 1.6 L + 0.5 ( L r or S or R ) .
Understanding which combination controls the design is a common requirement in PE exam problems.