public partial class MainWindow : Window
    {

        public double MyDurationDouble
        {
            get { return (double)GetValue(MyDurationDoubleProperty); }
            set { SetValue(MyDurationDoubleProperty, value); }
        }

        // Using a DependencyProperty as the backing store for MyDurationDouble.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty MyDurationDoubleProperty =
            DependencyProperty.Register("MyDurationDouble", typeof(double), typeof(MainWindow), new PropertyMetadata((o, e) => 
            {
                (o as MainWindow).DurationRefresh();
            }));



        void DurationRefresh()
        {
            MyDuration = new Duration(TimeSpan.FromSeconds(MyDurationDouble));
        }

        public Duration MyDuration
        {
            get { return (Duration)GetValue(MyDurationProperty); }
            set { SetValue(MyDurationProperty, value); }
        }

        // Using a DependencyProperty as the backing store for MyDuration.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty MyDurationProperty =
            DependencyProperty.Register("MyDuration", typeof(Duration), typeof(MainWindow), null);

        public MainWindow()
        {
            InitializeComponent();
            this.DataContext = this;


        }

<Window.Triggers>
        <EventTrigger SourceName="cmd1" RoutedEvent="Button.Click">
            <BeginStoryboard Name="Stb1">
                <Storyboard>
                    <DoubleAnimation
                        Storyboard.TargetName="Anm1" Storyboard.TargetProperty="Width"
                        From="40" To="400" Duration="{Binding MyDuration,Mode=TwoWay}"></DoubleAnimation>
                </Storyboard>
            </BeginStoryboard>
        </EventTrigger>
    </Window.Triggers>
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="50"></RowDefinition>
            <RowDefinition Height="*"></RowDefinition>
        </Grid.RowDefinitions>

        <TextBox Width="40" Height="50" VerticalAlignment="Top" HorizontalAlignment="Left" Text="{Binding MyDurationDouble,Mode=TwoWay}"> </TextBox>
        <Grid Height="111" Grid.Row="1">
            <Button Content="Button" Height="29" HorizontalAlignment="Left" Margin="18,14,0,0" Name="Anm1" VerticalAlignment="Top" Width="40" />
            <Button Content="Button" Height="29" HorizontalAlignment="Left" Margin="18,62,0,0" Name="cmd1" VerticalAlignment="Top" Width="144" />
        </Grid>
    </Grid>
</Window>