References
ACI 318-14
Mild Reinforcement
The development length of mild reinforcement is calculated individually for each bar and line wire following section 25.4 of ACI 318-14. The development length is calculated at the end of each reinforcement entity using the end point’s calculated spacing and cover. When computing the spacing for the given entity, only similar reinforcement types are considered. For example, when computing the development length for a piece of rebar, the spacing calculation only considers the nearest piece of rebar and will ignore nearby strand and mesh.
Straight Ends
Straight end tension development length is computed per ACI 318-14 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 uses both above equations and uses the minimum development length of the two. For equation 25.4.2.3 to be accurate the user must input a value for Ktr as leaving this term equal to the default value of zero can be conservative. The confinement term, Ktr, can be difficult for the program to compute as transverse reinforcement more or may not be present. 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
The development length of standard hooks in tension is computed per ACI 318-14 section 25.4.3. The confining reinforcement modification factor, 𝜓r, is assumed to be equal to 1.0. This is a conservative assumption and can be made per section 25.4.3.2. 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
Development length of headed bars in tension is computed per ACI 318-14 25.4.4. The conditions below, from section 25.4.4.1 are checked and if any are not satisfied the tension development length is computed as if it had straight-ends. The conditions below are not all the conditions listed in section 25.4.4.1, just all the Eriksson Beam is able to check.
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.
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 ACI 318-14 25.4.6 for deformed wires and 25.4.7 for plain wires. When computing development length, the first cross wire location is assumed to be located at the cross wire spacing into the line wire. This is a conservative assumption but is the maximum distance it can be from the end of the line wire for the cross wire spacing the be satisfied.
Compression Development Length
Development length of both bars and line wires in compression is computed using ACI 318-14 section 25.4.9 and assumes the confining reinforcement modification factor is 1.0.
Prestressed Reinforcement
Strand development length is computed using ACI 318-14 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 center of the strand (typically midspan) 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 minorly increases the development length. Debonded strand should double the development length per ACI 318-14 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. The development length above depends on whether the bar is in tension or compression. For strand, the effective area of the strand depends on what you are using strand for. For stress percent developed is computed the same way as mild reinforcement but using the transfer length in place of the development length. For ultimate computations, the development behaves bilinearly and can be seen in ACI 318-14 figure R25.4.8.3.