Loads and Load Combinations (NSCP) - Concept Map
Structural Loads and NSCP Load Combinations
Related concepts
Load Types
Sub concepts
- Dead Load (D)
- Live Load (L)
- Roof Live Load (Lr)
- Wind Load (W)
- Earthquake Load (E)
- Rain Load (R)
Relationship to central
Foundation — identifies what forces act on structures
Load Distribution
Sub concepts
- Tributary Area
- Tributary Width
- Line Load Calculation
- Axial Load Calculation
Relationship to central
Method — converts area loads to member forces
LRFD Design Philosophy
Sub concepts
- Gravity Combinations
- Wind/Seismic Combinations
- Uplift Combinations
- Resistance Factor φ
Relationship to central
Primary approach — ultimate strength with load factors
ASD Design Philosophy
Sub concepts
- Service Load Combinations
- Wind/Seismic Combinations
- Safety Factor Method
- Companion Live Load Factor f₁
Relationship to central
Alternative approach — allowable stress with reduction factors
Code Provisions
Sub concepts
- Load Case Selection
- Factor Application
- Minimum Load Values
- Occupancy Classification
Relationship to central
Regulatory framework — NSCP 2015 requirements
Application & Analysis
Sub concepts
- Beam Design Loads
- Column Axial Loads
- Design Moment Calculation
- Governing Combination Selection
Relationship to central
Execution — determination of design loads for members
Concept connections
- Load TypesLoad DistributionLoad types (D, L, W, E) are the inputs; distribution (tributary area) routes them to members
- Load DistributionLRFD Design PhilosophyDistributed member loads are factored using LRFD multipliers to obtain ultimate design forces
- Load DistributionASD Design PhilosophyDistributed member loads remain at service level and are combined per ASD rules
- LRFD Design PhilosophyCalculation MethodsLRFD factored loads are used to compute design moment, shear, and axial forces (Mu, Vu, Pu)
- ASD Design PhilosophyCalculation MethodsASD service loads are used to compute service moment, shear, and axial forces (M, V, P)
- Calculation MethodsCode ProvisionsDesign forces are checked against NSCP 2015 member strength (LRFD) or allowable stress (ASD)
- LRFD Design PhilosophyASD Design PhilosophyBoth are acceptable; must be chosen at project start and applied consistently; LRFD is preferred in modern practice
- Code ProvisionsLoad TypesNSCP 2015 tabulates minimum load values (kPa) for each occupancy type (residential, commercial, educational, etc.)
- Tributary Area ConceptLine Load CalculationTributary width is the spacing between adjacent beams; multiplied by slab load (kPa) to get line load (kN/m)
- Tributary Area ConceptAxial Load CalculationTributary area is the region closer to a column than to adjacent columns; multiplied by slab load to get column axial load (kN)
- Load FactorsGravity CombinationsFactors 1.2 on D and 1.6 on L are applied in the primary LRFD gravity combo 1.2D + 1.6L
- Load FactorsUplift CombosThe 0.9 factor on D in combos 0.9D + 1.0W and 0.9D + 1.0E captures uplift/overturning when dead load resists lateral forces
- Wind Load WWind & Seismic (LRFD)Wind load W is factored by 1.0 in combo 1.2D + 1.0W + 1.0L; also appears in uplift combo 0.9D + 1.0W
- Earthquake Load EWind & Seismic (LRFD)Seismic load E is factored by 1.0 in combo 1.2D + 1.0E + 1.0L; critical in seismic PH; also in uplift combo 0.9D + 1.0E
- NSCP 2015 RequirementsLoad TypesNSCP Section 202 defines load categories and minimum values for D, L, Lr, W, E, R based on occupancy and location
- Design Philosophy SelectionCalculation MethodsChoice of LRFD or ASD determines how loads are factored and how forces are calculated and compared to capacity
- Simply Supported BeamDesign Moment CalculationFor a simply supported beam of span L under UDL w, the maximum moment is M = wL²/8; basis for many exam problems
- Column Axial LoadMulti-Story StackingColumn loads accumulate from story to story; roof column carries roof + one floor; lower columns carry more stories
- Occupancy ClassificationLoad TypesOccupancy type (residential, office, assembly, etc.) determines the minimum live load L to be applied per NSCP Table
- Companion Live Load Factor f₁ASD Design PhilosophyIn ASD, f₁ = 1.0 for assembly/garage or L > 4.8 kPa; f₁ = 0.5 for residential/office; reduces combined-load combos to account for low probability of simultaneous max occupancy and wind/seismic
Diagrams
Loads and Load Combinations—Complete Concept Hierarchy
Comprehensive mind map showing the complete hierarchy of loads and load combinations. The central topic branches into six major areas: Load Types (defining what forces act), Load Distribution (how forces reach members), LRFD and ASD philosophies (two design approaches), Calculation Methods (finding design forces), NSCP requirements (Philippine code standards), and factor application principles. Each branch further subdivides into specific concepts and values used in structural design.
Load Combination Selection Process (LRFD vs ASD)
Decision flowchart showing the systematic approach to selecting and applying load combinations. The process begins with load identification, branches into LRFD or ASD philosophy selection, lists the primary combinations for each method, calculates design forces, identifies the governing (most severe) combination, and concludes with the appropriate design approach. This mirrors the decision-making process used in professional structural design and board exams.
Tributary Area & Load Distribution to Members
Flowchart illustrating how distributed loads on slabs are converted into member-level loads through tributary area concepts. Shows the distinction between interior and edge members (beams get different tributary widths), and between edge and interior columns (areas divided into quarters vs full). Demonstrates the path from slab loading in kPa through tributary geometry to member loads in kN/m (beams) or kN (columns), then to factored/service values for design.
LRFD Load Combination Hierarchy & Governing Selection
Comprehensive flowchart of all LRFD combinations showing how different load cases are organized into six categories (gravity, roof/rain, wind, seismic, uplift) and calculated. Shows that design forces (moment, shear, axial) from each combination are computed and compared; the maximum controls strength capacity while the minimum controls uplift and stability checks. This reflects the practical board-exam approach of comparing results across all applicable combinations.
ASD Load Combination & Service Design Process
ASD design process showing the seven primary service load combinations organized by type (basic, wind/seismic, combined). Emphasizes the live load factor f₁ distinction (1.0 for assembly and high-load areas, 0.5 for residential/office), which is critical for exam problems. Shows how service-level forces are compared to allowable stresses divided by a safety factor—the inverse of LRFD's factoring-up approach.
Design Load Evolution: From Slab to Member to Design
State diagram showing the progression of structural design from initial site loads through tributary distribution, philosophy selection (LRFD vs ASD), factor application, force calculation, combination comparison, and final design check. Illustrates that both methods arrive at verified member capacity, but via different paths (factored vs service) and final checks (strength with φ vs allowable with FS).
LRFD Load Factor Distribution in Typical Gravity Combo
Pie chart decomposing a typical LRFD gravity load combination (1.2D + 1.6L). If the unfactored dead load is D and live load is L, this shows the relative contribution of each when factored: the 1.6 multiplier on live load gives it greater weight, making live load govern most interior floors. Proportions assume D ≈ 40% and L ≈ 60% of typical office/residential floor loading. Useful for understanding why LRFD's 1.6 factor on L reflects the variability and criticality of occupancy loads.