Development Length
Codes
ACI 318-14
ACI 318-19
Mild Reinforcement
The development length of mild reinforcement is calculated individually for each bar and wire following Section 25.4 of ACI 318-14 / ACI 318-19. The development length is calculated from the end of each reinforcement object using the end point’s calculated spacing and cover. The development length is also calculated individually for each wire in a WWR sheet and not computed once for the entire sheet.
When computing the spacing for the given object, only similar reinforcement types are considered. For example, when computing the development length for a rebar, the spacing calculation only considers the nearest rebar and will ignore nearby strand and mesh.
Straight Ends
Code Provisions
ACI 318-14/19: Section 25.4.2
The development length of straight ends in tension is computed per Section 25.4.2. Per this provision, the base length can be computed using either Equation 25.4.2.2 or Equation 25.4.2.3. Eriksson Beam checks both equations and uses the minimum of the two computed values. For Equation 25.4.2.3 to be accurate the user should input a value for Ktr as leaving this term equal to the default value of zero can be overly conservative. The confinement term, Ktr, can be difficult for the program to compute as transverse reinforcement is typically difficult to detect programmatically without considerable additional input from the user. When using Section 25.4.2.2, a conservative assumption is made by ignoring the following condition: “Clear spacing of bars or wires being developed or lap spliced not less than db, clear cover at least db, and stirrups or ties throughout ℓd not less than the Code minimum.”
Hooked Ends
Code Provisions
ACI 318-14/19: Section 25.4.3
The development length of standard hooks in tension is computed per Section 25.4.3. The confining reinforcement modification factor, 𝜓r, is controlled based on a user input found on the Design Criteria. The cover modification factor, 𝜓c, can be reduced from 1 to 0.7 if the following is true: “For No. 11 bar and smaller hooks with side cover (normal to plane of hook) ≥ 2-1/2 in. and for 90-degree hook with cover on bar extension beyond hook ≥ 2 in.” When interpreting the clause above, Eriksson Beam assumes that the hook direction is vertical, so when checking the side cover (normal to plane of hook) it checks in the left and right directions. It also uses the bars start and end position is equal to the cover on the bar extension beyond the book. For example, an Inverted T with hooked ends starting 2 inches into the member will use 2 inches as the start cover.
Headed Bars
Code Provisions
ACI 318-14/19: Section 25.4.4
The development length of headed bars in tension is computed per 25.4.4. When computing the development length, the software checks 25.4.4.1 to determine if the use of a head to reduce the development length is valid. If it is not, it is computed as if it had a straight-end. These conditions are not all the conditions listed in Section 25.4.4.1, just all that Eriksson Beam is able to check with the current input.
ACI 318-14
Bar yield strength shall not exceed 60 ksi.
Bar size shall not exceed #11.
Concrete shall be normal weight.
Clear cover for bar shall be at least two times the bar diameter.
Clear spacing between bars shall be at least four times the bar diameter.
ACI 318-19
Bar size shall not exceed #11.
Concrete shall be normal weight.
Clear cover for bar shall be at least two bar diameters.
Center-to-center spacing between bars shall be at least 3 bar diameters.
When using ACI 318-19, the parallel tie reinforcing factor uses the same user input as hooked ends to determine what the factor should be.
Mechanically Anchored
The development length of mechanically anchored bars in tension and compression is assumed to be 0.
Wires
Development length of wires in tension is computed using 25.4.6 for deformed wires and 25.4.7 for plain wires. When computing development length, the first cross wire location is conservatively assumed to be located at a distance equal to the cross wire spacing.
Compression Development Length
Development length of both bars and wires in compression is computed using Section 25.4.9 and assumes the confining reinforcement modification factor is 1.0.
Prestressed Reinforcement
Strand development length is computed using Section 25.4.8. The development length is a function of the effective stress in the strand after losses and the stress in the strand at ultimate. The effective stress after losses is computed at the mid-point of the strand (typically the midspan of the concrete member) and uses the corresponding prestress losses at the same location. The stress at ultimate is assumed to be equal to the ultimate stress in the strand which is a conservative assumption that may increase the development length slightly. Debonding the strand doubles the development length per Section 25.4.8.1b which Eriksson Beam handles by using the debonded strand development length multiplier.
Development Length Multipliers
Multiple development length multipliers can be defined by the user. These include multipliers for mild reinforcement, strand, and debonded strand. For mild reinforcement, the multiplier is applied to both the compression and tension development length. For strand, the multiplier is applied to both the development length and the transfer length.
Effective Area of Partially Development Reinforcement
The area of reinforcement at a given location is reduced in areas where the reinforcement is not fully developed. For mild reinforcement, the percent developed at a given location is equal to that locations distance from the end of the bar divided by the given bar’s development length. For strand, the effective area calculation of the strand depends on the analysis type. For a stress analysis, percent developed is computed the same way as mild reinforcement but using the transfer length in place of the development length. For an ultimate analysis, the development length is calculated based on a bilinear development model that is shown in Figure R25.4.8.3.