In recent years, horizontally curved steel I-beams have become increasingly popular due to their use in modern buildings and highway bridges. However, the curvature in these beams create stability issues and significantly reduce the beam’s capacity. Moreover, the second-order effects become more pronounced as the curvature increases, leading to the fact that the curved beams carry relatively lower loads than equivalent straight beams. Therefore, it is crucial to accurately estimate the design capacities of such beams by appropriately accounting for the effects of curvature. An essential part of estimating the ultimate strength of beams using material and geometric nonlinear analyses is the correct assumption of initial residual stresses. The magnitude and distribution of residual stresses formed from hot-rolling or welding play a vital role in determining the imperfection factor to be used in the design strength equations. Whether heat-curving or cold curving, the curving process is further expected to change the assumed magnitude and distribution of residual stresses used in the beam design equations. However, current provisions in various international standards adopt the same residual stress pattern as that of straight I-beams for curved I-beams. Therefore, the present work incorporates the few scarcely documented residual stress patterns in literature for heat-curving as the initial stress state of the unloaded beam into finite element models. The studies compare the capacities of girders with these documented residual stresses for heat-curved I-beams with the capacities of the beams with assumed residual stresses typically assumed for equivalent straight I-beams. This paper highlights the need to measure experimentally the residual stresses formed due to heat-curving and its impact on estimating the strength of horizontally-curved I-beams.