We studied the upper-bound ultimate bearing capacity of smooth strip shallow footings with symmetrical and asymmetrical horizontal confinements on purely frictional sand within the framework of upper-bound limit analysis. The subsoil follows the associated flow rule, and no surcharge on the soil surface is assumed. The contact between the soil and the horizontal confinement walls is assumed to be perfectly rough. The upper-bound solutions for the objective functions are obtained using nonlinear sequential quadratic programming. The results for the different internal friction angles φ are provided in terms of the variation of two parameters, namely, the bearing capacity factor Nγ and the correction factor of bearing capacity Kγ, with respect to the change in the clear spacing between the edge of smooth footing and the rigid vertical walls. The values of Nγ and Kγ increase with φ and decrease with the clear spacing between the edge of the smooth footing and the rigid vertical walls. Nγ and Kγ are more sensitive to this confining effect as φ increases. The numerical results, a comparative analysis with the results from previous studies, and design charts are also included.