Concrete Design Reference

Q: What design code does this reference follow?

This reference is based on the Korean Design Standard (KDS 14 20), which is the national structural concrete design code for Korea. It covers strength reduction factors, load combinations, minimum cover requirements, reinforcement ratio limits, and all design formulas for flexure, shear, torsion, columns, and detailing consistent with KDS provisions.

Q: What material properties are included?

The reference covers concrete design compressive strength fck (24-100 MPa range with typical values for general buildings, high-rise, bridges, prestressed, and ultra-high strength), elastic modulus Ec = 8500*(fck+8)^(1/3), and three rebar grades: SD400 (fy=400 MPa), SD500 (fy=500 MPa), SD600 (fy=600 MPa), all with Es = 200,000 MPa.

Q: How is flexural design explained?

The flexural section covers singly reinforced beams with the complete formula chain (a = As*fy/(0.85*fck*b), Mn = As*fy*(d-a/2)) and a fully worked example (b=400, d=640, 3-D25, fck=27: a=66.2mm, Mn=369 kN.m, Mu=314 kN.m). It also covers doubly reinforced beams when Mu exceeds capacity, T-beam effective width, and one-way/two-way slab design including the direct design method (Mo = wu*L2*Ln^2/8).

Q: What shear design provisions are covered?

Concrete shear strength Vc = (1/6)*sqrt(fck)*bw*d, stirrup contribution Vs = Av*fyt*d/s, minimum stirrup requirement, maximum spacing rules (d/2 when Vs is small, d/4 when Vs exceeds (1/3)*sqrt(fck)*bw*d), torsion threshold and reinforcement formulas with Ao = 0.85*Aoh, and punching shear at the d/2 critical perimeter with three governing equations including the column aspect ratio beta factor.

Q: How is column design presented?

The column section explains the Pu-Mu interaction diagram with calculation points: pure compression (Pn0), balanced failure (cb = 600d/(600+fy)), and pure tension. It includes reinforcement ratio limits (1% minimum, 8% maximum, 1.5-4% practical range), tie spacing requirements, spiral reinforcement ratio, and slenderness effects with the moment magnification method (delta_ns >= 1.0, Cm factor, Euler critical load).

Q: What serviceability checks are covered?

Deflection limits are L/360 for immediate live load deflection and L/240 for long-term total load deflection. Minimum depths to avoid deflection calculation are provided: one-way slab L/20 (simply supported) to L/28 (continuous), beam L/16 to L/21. Crack width limits are 0.4mm (dry), 0.3mm (wet), and 0.2mm (corrosive environment) with the crack width formula w = 2*(fs/Es)*beta*sqrt(dc^2+(s/2)^2).

Q: Does it include seismic design requirements?

Yes. The reference covers special moment frame (SMF) requirements: beam maximum reinforcement ratio 0.025, minimum two continuous bars top and bottom, hoop spacing D10@100 in plastic hinge zones. For columns, the strong column-weak beam rule requires sum(Mnc) >= 1.2*sum(Mnb), with hoop spacing D10@100 in the Lo region where Lo = max(h, Ln/6, 450mm).

Free reference guide: Concrete Design Reference

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About Concrete Design Reference

The Concrete Design Reference is a searchable quick-reference tool for reinforced concrete structural design based on the Korean Design Standard (KDS 14 20). It covers material properties including concrete design compressive strength (fck from 24 MPa for general buildings to 100 MPa for ultra-high strength), elastic modulus calculation (Ec = 8500 * (fck+8)^(1/3)), and rebar specifications for SD400, SD500, and SD600 grades with Es = 200,000 MPa. Design code provisions include strength reduction factors (phi = 0.85 for flexure, 0.75 for shear, 0.65 for tied columns), ultimate load combinations, minimum cover depths, and minimum/maximum reinforcement ratios.

The flexural design section provides complete formulas for singly reinforced beams (a = As*fy/(0.85*fck*b), Mn = As*fy*(d-a/2)) with a worked numerical example, doubly reinforced beams when Mu exceeds phi*Mn_max, T-beam effective width calculations, and both one-way and two-way slab design methods including the direct design approach. The shear design section covers concrete shear strength (Vc = (1/6)*sqrt(fck)*bw*d), stirrup contribution (Vs = Av*fyt*d/s), maximum stirrup spacing rules, torsion design with threshold and reinforcement formulas, and punching shear verification at the critical section d/2 from the column face.

Column design entries explain the Pu-Mu interaction diagram construction from pure compression through balanced failure to pure tension, reinforcement ratio limits (1% minimum to 8% maximum, 1.5-4% recommended in practice), tie spacing requirements, and slenderness effects with moment magnification. The detailing section covers tension development length, splice length classes (A and B), standard hook development, and shear wall reinforcement ratios. Serviceability checks for deflection (L/360 immediate, L/240 long-term) and crack width (0.2-0.4 mm by environment), plus special moment frame seismic detailing requirements complete the reference.

Key Features

Material properties: concrete fck ranges from 24 to 100 MPa, Ec formula (8500*(fck+8)^(1/3)), SD400/SD500/SD600 rebar grades with Es = 200,000 MPa and yield strain calculation
KDS strength reduction factors: phi = 0.85 (flexure/tension-controlled), 0.70 (compression/spiral), 0.65 (compression/tied), 0.75 (shear/torsion), 0.65 (bearing), plus five ultimate load combinations
Complete flexural design formulas with worked example: b=400mm, d=640mm, 3-D25 bars, fck=27 MPa calculating a=66.2mm, Mn=369 kN.m, Mu=314 kN.m, plus T-beam effective width (min of L/4, bw+16hf, center spacing)
Shear design: Vc = (1/6)*sqrt(fck)*bw*d, Vs = Av*fyt*d/s, maximum stirrup spacing rules (d/2 or d/4 depending on Vs threshold), torsion threshold Tu formula, and punching shear at d/2 critical perimeter with three governing equations
Column Pu-Mu interaction diagram: Pn0 = 0.85*fck*(Ag-Ast)+fy*Ast, balanced failure depth cb = 600d/(600+fy), reinforcement limits 1-8%, tie spacing min of 16db, 48dt, and column minimum dimension
Slenderness check: KL/r < 22 (unbraced) or < 34-12(M1/M2) (braced), moment magnification delta_ns = Cm/(1-Pu/(0.75*Pc)) with Euler critical load Pc = pi^2*EI/(KL)^2
Reinforcement detailing: tension development length Ld with simplified formula, Class A splice (1.0*Ld) and Class B splice (1.3*Ld), standard 90-degree (12db extension) and 180-degree hooks (4db, min 65mm), shear wall min rho = 0.0025
Serviceability: deflection limits L/360 (live load) and L/240 (total), minimum slab/beam depths to avoid deflection calculation, crack width limits 0.2-0.4 mm by exposure, and special moment frame seismic requirements (strong column-weak beam 1.2 ratio, hoop at D10@100)

Frequently Asked Questions

What design code does this reference follow?

This reference is based on the Korean Design Standard (KDS 14 20), which is the national structural concrete design code for Korea. It covers strength reduction factors, load combinations, minimum cover requirements, reinforcement ratio limits, and all design formulas for flexure, shear, torsion, columns, and detailing consistent with KDS provisions.

What material properties are included?

The reference covers concrete design compressive strength fck (24-100 MPa range with typical values for general buildings, high-rise, bridges, prestressed, and ultra-high strength), elastic modulus Ec = 8500*(fck+8)^(1/3), and three rebar grades: SD400 (fy=400 MPa), SD500 (fy=500 MPa), SD600 (fy=600 MPa), all with Es = 200,000 MPa.

How is flexural design explained?

The flexural section covers singly reinforced beams with the complete formula chain (a = As*fy/(0.85*fck*b), Mn = As*fy*(d-a/2)) and a fully worked example (b=400, d=640, 3-D25, fck=27: a=66.2mm, Mn=369 kN.m, Mu=314 kN.m). It also covers doubly reinforced beams when Mu exceeds capacity, T-beam effective width, and one-way/two-way slab design including the direct design method (Mo = wu*L2*Ln^2/8).

What shear design provisions are covered?

Concrete shear strength Vc = (1/6)*sqrt(fck)*bw*d, stirrup contribution Vs = Av*fyt*d/s, minimum stirrup requirement, maximum spacing rules (d/2 when Vs is small, d/4 when Vs exceeds (1/3)*sqrt(fck)*bw*d), torsion threshold and reinforcement formulas with Ao = 0.85*Aoh, and punching shear at the d/2 critical perimeter with three governing equations including the column aspect ratio beta factor.

How is column design presented?

The column section explains the Pu-Mu interaction diagram with calculation points: pure compression (Pn0), balanced failure (cb = 600d/(600+fy)), and pure tension. It includes reinforcement ratio limits (1% minimum, 8% maximum, 1.5-4% practical range), tie spacing requirements, spiral reinforcement ratio, and slenderness effects with the moment magnification method (delta_ns >= 1.0, Cm factor, Euler critical load).

What reinforcement detailing is included?

Tension development length Ld with both the full formula and simplified versions for D19-D35 bars, Class A (1.0*Ld when As provided/required >= 2) and Class B (1.3*Ld) splice lengths with a D22 SD400 example, standard hook development (90-degree with 12db extension, 180-degree with 4db/65mm minimum), and shear wall reinforcement ratios (rho >= 0.0025 when Vu > Vcr, rho >= 0.0012 otherwise) with maximum spacing s <= min(3t, 450mm).

What serviceability checks are covered?

Deflection limits are L/360 for immediate live load deflection and L/240 for long-term total load deflection. Minimum depths to avoid deflection calculation are provided: one-way slab L/20 (simply supported) to L/28 (continuous), beam L/16 to L/21. Crack width limits are 0.4mm (dry), 0.3mm (wet), and 0.2mm (corrosive environment) with the crack width formula w = 2*(fs/Es)*beta*sqrt(dc^2+(s/2)^2).

Does it include seismic design requirements?

Yes. The reference covers special moment frame (SMF) requirements: beam maximum reinforcement ratio 0.025, minimum two continuous bars top and bottom, hoop spacing D10@100 in plastic hinge zones. For columns, the strong column-weak beam rule requires sum(Mnc) >= 1.2*sum(Mnb), with hoop spacing D10@100 in the Lo region where Lo = max(h, Ln/6, 450mm).