Accurate　evaluation　of　preload　in　system　with　double-bolted　connections　is　critical　for　the　service　performance　of　engineering　structures　or　equipment.　However,　the　theoretical　framework　for　assessing　preload　is　imperfect.　An　equivalent　approach　from　the　tightening　process　of　double-bolted　joints　to　second-order　spectral　problem　of　the　energy-dependent　potential　is　firstly　established.　This　paper　proposes　a　novel　nonlinear　model　of　bolt　preload　considering　physical　and　geometric　parameters　by　proving　the　completely　integrability　of　systems　used　bolted　connections.　The　experimental　device　for　hmeasuring　displacement　and　bolt　preload　was　developed　to　verify　the　accuracy　of　proposed　model.　Results　show　that　the　maximum　relative　error　is　not　more　than　3%.　Finally,　the　influences　of　elastic　modulus,　density,　holes　spacing,　and　height　on　preload　are　analyzed.　(c)　2021　Elsevier　Inc.　All　rights　reserved.