Highway　bridge　decks　are　susceptible　to　fatigue　failure　under　direct　and　repetitive　wheel　loading,　and　significant　live　load　effects　have　caused　increasing　concerns　in　bridge　engineering.　We　used　a　newly　constructed　rail-cum-road　steel　truss　bridge　as　a　case　study　to　study　the　initial　stress　state　and　stress　response　in　a　steel-concrete　composite　bridge　deck　under　a　long-term　vehicular　live　load.　Static　and　dynamic　load　tests　with　a　single　truck　passing　the　bridge　deck,　as　well　as　dynamic　load　cases　in　which　two　trucks　were　driving　on　the　deck　side　by　side,　were　performed.　The　strains　at　the　midspan　and　pier　sections　were　measured　using　embedded　vibrating　chord　and　resistance　strain　gauges　before　concrete　placement.　We　then　established　a　finite　element　model　of　the　bridge　to　analyze　the　structural　behavior　of　the　bridge　deck　under　various　loading　cases　of　the　field　test.　The　measured　strain　results　showed　that　the　initial　stress　states　of　the　concrete　deck　at　the　midspan　and　pier　sections　were　compression　and　tension,　respectively,　before　bridge　service.　The　tensile　strain　at　the　pier　section　reached　101.8　micro　strains　even　after　staged　construction,　indicating　a　cracking　risk.　The　testing　vehicle　caused　additional　compression　stress　for　the　majority　of　the　bridge　deck.　However,　the　live　load　stress　in　the　transverse　direction　near　the　main　truss　girder　was　tensile,　causing　it　to　experience　repetitive　live　load　stress　and　longitudinal　cracking　risk.　Because　the　length　of　the　influence　line　for　all　measuring　points　was　approximately　20　m　(less　than　two　truss　panels　long),　the　testing　truck　generated　one　major　stress　cycle　for　each　passing.　The　measured　strain　amplitude　caused　by　the　live　load　reached　a　maximum　of　34.6　micro　strains.　Because　the　bending　strain　exhibited　a　strain　gradient　along　the　deck　depth,　the　most　significant　strain　amplitude　on　the　top　or　bottom　surface　of　the　deck　was　51.9　micro　strains,　triggering　fatigue　failure　of　the　composite　deck.　The　stress　distribution　from　the　finite　element　analysis　coincided　well　with　the　measured　deck　strain　near　the　main　truss,　suggesting　that　the　model　could　be　employed　for　subsequent　fatigue　stress　analysis.　This　study　can　also　provide　data　and　a　reference　for　assessing　and　maintaining　composite　bridge　decks　in　similar　bridges.　©　2023　Xi＇an　Highway　University.　All　rights　reserved.