Grid view button click dont want to referesh grid

 <asp:UpdatePanel ID="UpdatePanel1" runat="server" >
            <ContentTemplate>
  <asp:Button ID="btnExpenseAccount" runat="server" CssClass="button_small_tgrid" Text="..."
                                                    Enabled="false" OnClick="btnExpenseAccount_Click" />
 </ContentTemplate>
 </asp:UpdatePanel>

protected void btnExpenseAccount_Click(object sender, EventArgs e)
        {
Button btn = (Button)sender;
UpdatePanel1.Triggers.Add(new AsyncPostBackTrigger { ControlID = btn.UniqueID, EventName = "click" });
}