insérer un usercontrol en code behind

<AjaxToolkit:TabContainer ID="tabs" runat="server" ActiveTabIndex="0" Height="380px" Width="784px" />

for (int i = 0; i < 5; i++)
            {
                TabPanel tab = new TabPanel();
                tab.Controls.Add(new UCPrevTabTH() { ID = "tab" + i.ToString() });
                PlaceHolder ph = new PlaceHolder() { ID = "ph" + i.ToString() };

                UCPrevTabTH uc = new UCPrevTabTH();
                uc = (UCPrevTabTH)LoadControl("UCPrevTabTH.ascx");
                uc.ID = "uc" + i.ToString();

                ph.Controls.Add(uc);

                tab.Controls.Add(ph);
                tabs.Tabs.Add(tab);
            }