As per your comment, I tried to run a simple test to check it out but it's working in my local. I tried:
1. My code-behind is something like:
protected void Page_Load(object sender, EventArgs e)
{
Session["TireLn"] = "test";
}
2. Accessing value as:
<script type="text/javascript">
$(document).ready(function () {
var a = '<%=Session["TireLn"]%>';
alert(a);
}
</script>
3. In Result, I'm getting "test" in alert on page load.
I think, you are doing something wrong in your code. Consider and check your code with above one. If you still having issue, provide important code that you are using here.