作者: Ronald W. Borst
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摘要: Improvements in plastic coated, steel core reinforced manhole steps; particular improvements the drive-in or hammer-in ends of a U-configuration step construction, which involve providing resilient, barb-like retainer elements yet relieving such patterns so as to enable debris and water formed holes escape order protect concrete against conveyed impact pressures further more effective sealing engagement with wall orifices; drive steps type wherein are relieved end portions thereof obviate prevent any recesses proper; wedge tooth barb configuration achieve maximum pullout resistance while retaining pressure material relief features.