Structural Design Fundamentals Quiz

Introduction to Structural Concrete Design

• This presentation introduces structural concrete design.
• The presenter is Jerome Z. Tadiosa, CE, MSc, an Assistant Professor 2 in Civil Engineering at National University-Manila.
• The course code is CEPRCD30 (Principles of Reinforced Concrete).

Intended Learning Outcomes

• Students will be able to describe the structural design process and associated considerations.
• Students will learn the description, development, and classification of structural concrete.
• Students will identify and describe design philosophies, relevant codes, and standards in structural concrete design.
• Students will identify and describe the materials used in structural concrete construction.

Reading Guide

• Required reading consists of Chapters 1-3 from the Wight (2016) textbook.
• Chapter 1 from the McCormac & Brown (2016) book.
• Sections 1.1-1.2 of Chapter 1 from the Salmon et.al. (2009) textbook.
• Additional references may be beneficial for better understanding.

Lecture Outline

• Introduction to the structural design process
• Introduction to structural concrete design
• Materials used in structural concrete design

Structural Design

• Structural design combines art and science, combining the intuitive feelings of an experienced engineer with established engineering principles.
• A properly designed structure should prioritize appropriateness (functionality and aesthetics), economy (optimal benefit-cost ratio, preferably minimum cost), structural adequacy (strength and serviceability requirements), and maintainability (minimum maintenance cost and time).

General Design Process

• The general design process includes crucial phases:
• Defining client needs and priorities: function, aesthetics, budget
• Developing the project concept: schematics, preliminary framework, materials
• Designing individual systems: structural analysis and design, utilities & other systems
• Structural design is iterative and sequential, with potential for multiple refinements.

Structural Design Process (Continued)

• Planning includes setting and finalizing project details.
• Preliminary structural configuration involves the initial layout of structural members.
• Establishment of loads depends on material properties, function, and site conditions.
• Preliminary member selection entails initial sizing of structural members.
• Structural analysis involves modeling and analyzing the structure to define forces and deformations.
• Evaluation verifies individual members against strength and serviceability, aligning with client specifications.
• Redesign may be needed based on evaluation results, leading to cycles until optimized.
• A final decision determines whether the current design iteration is optimum.

Structural Concrete

• Structural concrete is "plain or reinforced concrete" within a member, transferring loads directly to the ground.
• Concrete is a mixture comprising hydraulic cement, aggregates, water, and potentially admixtures, fibers, or other cementitious materials.
• Plain concrete has no reinforcement or less reinforcement compared to the minimum reinforcement standards for reinforced concrete.
• Reinforced concrete contains reinforcement to support tensile strength.
• Reinforced concrete is categorized as steel-reinforced concrete or prestressed concrete (using tendons).

Advantages of Structural Concrete

• High compressive strength
• Excellent resistance to fire and water damage
• Rigidity and durability
• Low maintenance costs
• Long service life
• Cost-effectiveness for substructures and floor slabs
• Moldability
• Relatively low labor skill requirements needed for construction

Disadvantages of Structural Concrete

• Relatively low tensile strength
• Formworks are required
• Low strength-to-weight ratio
• Variations in properties due to mixing consistency

Historical Background of Concrete

• Lime mortar was initial form, used in Minoan civilization.
• Romans innovated with volcanic ash (pozzolana) for stronger, water-resistant mortar.
• John Smeaton developed water-resistant mixes of limestone and clay.
• Joseph Aspdin created Portland cement by heating limestone and clay.
• Other individuals (W. B. Wilkinson, Joseph Lambot, Thaddeus Hyatt, Joseph Monier, W. E. Ward, and E. L. Ransome) contributed key milestones in the development of structural concrete design.

Limit States

• Limit states define conditions when a structure or a structural member is unfit for its intended use.
• Three basic categories include strength limit states, serviceability limit states, and special limit states.

Limit States Design

• The process involves identifying all possible failure modes or limit states.
• Establishing appropriate safety levels for each limit state.
• Evaluating structural designs considering the significant limit states.
• Using the ultimate strength design (USD) method for structural concrete design.
• This method mandates multiplying service loads by load factors and multiplying computed nominal strengths by strength reduction factors. This approach addresses variability in material properties and load intensity.

Strength Design Method

• Structural design requires member capacity to be greater than the member demand.
• This principle applies to structural members subjected to load effects under the ultimate strength design (USD) method.
• Key variables include strength reduction factors (Ø), nominal member strength (Rn), total factored load (Qu), and load factors for various load types (Y₁, Q₁).

USD Load Combinations

• Factored load combinations must be applied to the structure in accordance with specific design standards (e.g., 2015 NSCP) during design calculations.
• Specific combinations are provided by the design codes for different loading conditions.
• Accurate calculations are essential to achieve safe and reliable structures.

Service Load Combinations

• Service loads must be combined in accordance with specific standards during design.

Structural Safety

• The establishment of load factors and strength reduction factors are to address variability in material properties, section dimensions, and load intensity.
• To account for consequences of failure, with potential losses in life and property.

Codes and Standards for Structural Concrete

• Codes and standards for structural concrete design typically include The 2015 National Structural Code of the Philippines (NSCP), various ACI codes (318M-14, 318R-14), and other associated documents.

Design for Economy

• Economy prioritizing minimizing costs while maintaining structural integrity.
• Focus on efficiency for various materials and formwork.
• Simplifying the design and employing consistent column sizes helps maintain economic balance.

Design for Sustainability

• Durable construction contributes to sustainability, focusing on long-term economic and environmental benefits.
• Durability also yields reduced lifecycle costs and energy usage.

Materials for Structural Concrete Construction

• Concrete is a composite material composed of aggregates (coarse and fine) and cement, water, and admixtures.

Concrete

• The cement paste in concrete acts as a binding agent between aggregates.
• Concrete is strong in compression but weak in tension, thus reinforcement is crucial.
• The non-linear stress-strain relationship of concrete reveals its ductile behavior due to microcracking under load. Mix design utilizes traditional proportions, modified based on DPWH (Department of Public Works and Highways) guidelines or relevant ACI standards.

Mechanism of Concrete Failure in Compression

• Failure occurs in stages during uni-axial loading, starting with no-load bond cracks due to shrinkage, which progresses to the development of aggregate bond cracks and ultimately mortar cracks.

Compressive Strength of Concrete

• Concrete compressive strength is based on standard testing procedures outlined in ASTM C31 and C39.
• Testing typically occurs at 28 days after curing.

Factors Affecting Concrete Compressive Strength

• Water-cement ratio (lower is better), type of cement (e.g., Type I, Type III), and curing conditions (moisture and temperature).
• Other factors include supplementary cementitious materials like fly ash and ground granulated blast-furnace slag, aggregate properties (strength, grading, quality, and toughness).
• Mixing water (potable is preferable) also plays a role.

Tensile Strength of Concrete (Modulus of Rupture)

• Determining tensile strength involves performing testing in accordance with ASTM C78 and ASTM C496 standards.

Modulus of Rupture

• Calculated using suitable equations (e.g., fr = 0.622√fc).

Factors Affecting Tensile Strength of Concrete

• Similar factors to those influencing compressive strength also affect tensile strength; crushed rock aggregates usually result in higher tensile strength.

Stress-Strain Curve of Concrete in Compression

• Stress-strain relationships provide insights into the material's behavior under compressive loading.

Modulus of Elasticity and Poisson's Ratio of Concrete

• The modulus of elasticity (Ec) is typically calculated using equations based various design standards (e.g., Ec = 4700√fc).

Time-Dependent Volume Changes: Shrinkage

• Drying shrinkage occurs as water evaporates from the concrete surface.
• Autogenous shrinkage is related to water loss associated with hydration reactions.
• Carbonation shrinkage happens in carbon dioxide rich environments.

Time-dependent Volume Changes: Creep

• Creep is a time-dependent material deformation under sustained and/or elevated temperatures.
• Creep strains develop as the loads are applied longer.

Time-dependent Volume Changes: Thermal Expansion

• Thermal expansion of concrete depends on the aggregate type (Siliceous, Limestone, Lightweight concrete, general coefficients), moisture content (higher for higher humidity), and concrete age (typically higher for newer concrete).

Durability Issues in Concrete Structures

• Corrosion of steel reinforcement requires moisture and oxygen for oxidation.
• Proper concrete protection measures (e.g., air entrainment, minimum W/C ratio, minimum cover) avoid adverse affects of freezing and thawing.
• Chemical attacks (e.g., sulfate attack) necessitate appropriate cement selections and aggregate sources.

Extreme Temperature Behavior of Concrete

• High temperatures can cause damage; expansion, cracks, and spalling occur during the fire.
• The temperature-dependent behavior of concrete with various aggregates types during heat exposure and cooling is notable.
• Low temperatures also influence concrete behavior and strength and are less impactful compared to high temperature situations.

Steel Reinforcement

• Steel reinforcement is a defined structure in concrete to reinforce tensile strength.
• Hot-rolled deformed bars, welded wire fabric and steel tendons are common types.
• Using fibers within the matrix is a very recent reinforcement type.

Hot-Rolled Deformed Bars

• Manufacturing specifications are standardized regarding tensile strength, yield strength, and elongation capacity.
• Grades are available (Grade 33 ~ 75).
• Bars are available in various diameters and sizes.

Hot-Rolled Deformed Bars: Fatigue Strength

• Fatigue assessment and the use of stress-strain relationships are important to account for failure conditions under repeated loads.

Hot-Rolled Deformed Bars: Strength at High Temperatures

• Elevated temperatures reduce yield and ultimate strengths.

Compatibility of Concrete and Steel

• Concrete supports compressive stress while reinforcement supports tensile stress.
• Durability considerations are essential for the compatibility of the two materials.

References

• Multiple sources provide information regarding structural concrete design, codes, and standards, which includes various books, and institutions.

Test your knowledge on the primary objectives and phases of structural design. This quiz covers essential concepts such as structural adequacy, design criteria, and the importance of client needs. Challenge yourself with questions about design philosophies and relevant codes in structural concrete design.