[HttpPost]
        public ActionResult getRequirmentsByProject(string projectname)
        {

            return Json(projectname, JsonRequestBehavior.AllowGet);
        }

var projectname = document.getElementById('projName').value;
    $.ajax({
        url: '/Worksheet/getRequirmentsByProject',
        type: 'post',
        data: { projectname },
        contentType: 'application/json; charset=utf-8',
        success: function (html) {
            alert(html);
        },
        error: function (error) {
            $(that).remove();
            DisplayError(error.statusText);
        }
            });