open drainopen end wellopen fireopen gradedopen hearthopen heateropen inletopen pit miningopen roofopen sectionopen spaceopen texturedopen tread stairopen trussed structureopen web beamopen web joistopen wellopeningopening jointoperatingoperating bridgeoperating conditionsoperating costoperating engineeroperating headoperating platformoperating pointoperationoperation analysisoperational delayoperational freeboardoperational researchoperational wastesoperativeoperatoroperator of heavy machineryoperator of light machineryopportunity modeloptical axisoptimal designoptimistic estimateoptimizationoptimumoptimum asphaltoptimum depth of cutoptimum designoptimum directionoptimum maximum angleoptimum moistureoptimum moisture content
