In Angular ui-router nested state url changes,but template is not loading

Your nested project.settings state needs to address the view in the higher state explicitly using an ‘@’ suffix, ie.:

.state('project.settings', {
        url: "/settings",
        views:{
              "content@":{templateUrl: "partials/project.settings.html"},
              "header@":{templateUrl: "partials/header"}
        }
 }) 

See more details here https://github.com/angular-ui/ui-router/wiki/Multiple-Named-Views#view-names—relative-vs-absolute-names