Safety demands rebar connection design

End anchorages involve connecting new concrete elements perpendicular to existing ones. Examples include beam-to-column, slab-to-wall, column-to-foundations, and so on.

Lap splices involve extending existing concrete elements parallel to existing ones. The new bars are not in contact with existing ones. Examples include beam extension, column extension, slab extension etc.​

Concrete overlays involves increase the cross-sectional thickness of an existing member by connecting a new layer. Examples include beam jacketing, column jacketing, slab strengthening etc.​

For end anchorages, once the design of the new section and required reinforcement is complete, calculation of the development length, ld, is required to safely transfer the stress in the bar to existing concrete member. This is undertaken with the same provisions for cast-in bars as in Chapter 25 of ACI 318-14 & -19.

Additional checks involve complying with requirements such as the project’s design or service life, and the minimum development length requirements of ACI 318.

For lap splices, once the design of the new section and required reinforcement is complete, calculation of the development length, ld, is required to safely transfer the stress in the bar to the bars in the existing concrete member. This is undertaken with the same provisions for cast-in bars as in Chapter 25 of ACI 318-14 & -19.

Additional checks involve complying with requirements such as the project’s design or service life, and the minimum development length requirements of ACI 318.

Design follows the provisions of Chapters 22 and 25 of ACI 318-14 & -19 and is centered on calculating the resistance of the entire interface based on the contributions of friction and the full yield strength of the dowel action of the bar. Based on the modified shear-friction theory, increasing roughness results in increased friction that reduces the number of required bars crossing the interface.

The designer must specify the roughness class desired at site since this strongly influences the design. The roughness class may be determined by the “sand patch” or “mean depth” methods, or through optical profilometry.

Static Design​

This is the most common class of applications for post-installed rebars and includes the connection of new components to an existing structure. According to structural concrete building codes, the bond strength of cast-in bars is limited, even where depth of concrete cover is considerable. And so, in some areas, such as walls where anchorage depth is often limited, welded transverse reinforcement or hooks are used to compensate for the reduction in available anchorage length.​

Seismic Design​

An increasing population density, the concentration of valuable assets in urban centers and society’s dependence on a functioning infrastructure demand a better understanding of the risks posed by earthquakes. In several areas around the globe, these risks have been reduced through appropriate building codes and state of the art construction practices. The development of pre-qualification methods to evaluate building products for seismic conditions additionally contributes to safer buildings for generations to come.​

Fire Design​

Organic adhesives are affected by high temperatures. For post-installed rebar connections that are part of a fire-resisting assembly (floor, roof, etc.), evaluating the fire resistance of the connection is key to ensure safety. Currently, AC308 does not have the provisions to qualify a mortar to elevated temperatures. However, designers may find the European equivalent (EAD 330087) relevant as it provides a time-dependent reduction in bond strength associated with typical geometries and time-temperature loading protocols for specific assessed mortars.