Abstract: The portable tensioning system takes the place of permanently installed facilities including massive earth anchors for casting pre-stressed building units such as concrete beams. Such permanently installed casting beds must be demolished if they are to be subsequently removed. The portable system comprises a plurality of pre-cast modular segments with walls defining channels to serve as part of a casting bed. These segments are provided with longitudinal bores so that they can be transported to a building site, aligned in end to end relationship, and post-tensioned by passing strands through the aligned bores to provide an overall elongated casting bed. After the casting operation has been completed, the segments can be disassembled and transported to another site for re-use.