RCD Midterms

Strength Design Method

Primary method used in the National Structural Code of the Philippines (NSCP) 2015 for designing reinforced concrete structures

Nominal strength

strength based on dimension and material property

Required Strength

This is the load effect on the structure, calculated by applying load factors to the service loads (dead load, live load, wind load, etc.).

Reduction Factor

This factor is less than 1 and accounts for uncertainties in material properties, construction quality, and analysis methods.

Strength Design Method

method of proportioning and designing structural members such that the computed forces produced in the members by the factored loads do not exceed the member design strength.

Allowable stress design

also known as working stress or design stress method (WSD), is the maximum stress a material or structure can withstand under normal operating conditions without failing.

Allowable Stress Design

method of proportioning and designing structural members such that elastically computed stresses produced in the members by nominal loads do not exceed specified allowable stresses.

Loads

Forces or other actions that result from the weight of all building materials, occupants and their possessions, environmental effects, differential movements and restrained dimensional changes.

0.003

Maximum strain at the extreme concrete compression fiber

Tensile strength

neglected in flexural and axial strength calculations

On Strain

Plane sections remain plane; it varies linearly from the maximum compressive strain at top fiber to the tensile strain at bottom reinforcement.

On Stress

Stress on beams is represented by a parabolic distribution along the compression zone.

Nominal Moment Capacity

Maximum bending moment without any safety factors

Ultimate Moment Capacity

Maximum bending moment with safety factors; Moment Due to Factored Loads; Factored Design Moment; Design Strength

Strength Reduction Factor

A coefficient used to provide a margin of safety in Ultimate Strength Design

Coefficient of Resistance

A coefficient used to relate the member’s capacity with its geometric properties or dimensions

b

width of compression face of member or width of beam for rectangular section

D

Overall depth of the beam

d

effective depth of beam

c

distance from extreme compression fiber to neutral axis , mm; depth of compression block

a

depth of equivalent stress block, mm ; depth from the outermost compression fiber to the equivalent end of compression fiber

fs

calculated stress in the reinforcement in service loads

f’c

specified compressive stress of concrete

w

reinforcement index ratio ; the ductility or failure mode of member

p

ratio of tension reinforcement or steel ratio ; the proportion of tension reinforcement to the effective concrete area ; ensures balance on steel reinforcement against the effective area of beam

Steel Ratio

It is a critical parameter that determines the structural behavior, strength, and failure mode of a member.

It balances the concrete's compressive strength with steel's tensile strength, ensuring that structures are safe, durable, and economical.

Balanced condition

The maximum strain at the extreme concrete compression fiber just reaches the crushing strain εc = 0.003 at the same time as the tension steel reaches a strain εs = fy / Es causing them to fail simultaneously.

Compression controlled

Concrete may fail before the yield of steel due to the presence of high percentage of steel in the section more than what is required for balanced condition.

The strain in the steel is equal to or less than 0.002

Tension controlled

Steel may reach its yield strength before the concrete reaches its maximum strength, in this case, the failure is due to the yielding of steel reaching a high strain equal to or greater than 0.005

Non-rectangular beam

Any structural beam with a cross-sectional shape that is not a simple rectangle

Complex analysis

The analysis for non-rectangular beams is more complex because the compression stress block's shape can be irregular, and the neutral axis may be located either in the flange or the web.

Steel reinforcement

The amount and placement of steel reinforcement are crucial for a beam's strength and stability.

Non-rectangular beams can be doubly reinforced with steel in both the tension and compression zones to increase their ultimate moment capacity

T beams

Simple beams that are shaped like a letter T, with extra widths at the top called flanges

Normally consisting of floor slabs and beams that are casted monolithically that results to two parts, working together to resist a load.

Doubly Reinforced Beam

A type of beam which is reinforced both in tension and compression zone

Continuous beams

In ____________, specially at the supports where bending moment is often negative, compression steel is needed to resist the compression forces

Cc

compressive force of concrete

Cs

compressive force of steel

As

area of non-prestressed longitudinal tension reinforcement

A’s

Steel area of compression reinforcement

d’

distance of compression fiber to centroid of compression reinforcement