$(".initial_cap").keydown(function(){
        console.log("aaa");
        var val = $(this).val();
        if(val.length==1)
        {
            val = val.charAt(0).toUpperCase() ;
            $(this).val(val);
        }
    });

<input class="form-control initial_cap" placeholder="Address1" required="required" maxlength="50" name="address1" type="text" value="" aria-required="true">