<Grid x:Name="LayoutRoot" Background="White">
        <sdk:TabControl Height="100" HorizontalAlignment="Left" Margin="72,136,0,0" Name="tabControl1" VerticalAlignment="Top" Width="200">
            <sdk:TabItem Header="tabItem1" Name="tabItem1">
                <Grid />
            </sdk:TabItem>
        </sdk:TabControl>
        <Button Content="Button" Height="23" HorizontalAlignment="Left" Margin="118,44,0,0" Name="button1" VerticalAlignment="Top" Width="75" Click="button1_Click" />
    </Grid>

public MainPage()
        {
            InitializeComponent();
            TabItem ti = new TabItem();
            tabControl1.Items.Add(ti);
            Grid g1 = new Grid();
            g1.Name = "g1";
            ti.Content = g1;
            Grid g2 = new Grid();
            g2.Name = "g2";
            g1.Children.Add(g2);
            object o1 = FindName("g1");
            object o2 = FindName("g2");
        }

        private void button1_Click(object sender, RoutedEventArgs e)
        {
            TabItem ti = new TabItem();
            tabControl1.Items.Add(ti);
            Grid g3 = new Grid();
            g3.Name = "g3";
            ti.Content = g3;
            Grid g4 = new Grid();
            g4.Name = "g4";
            g3.Children.Add(g4);
            object o1 = FindName("g3");
            object o2 = FindName("g4");
        }