how to give an elevation to a ConstraintLayout which has a vector background

Question

I have a ConstraintLayout with a vector background. I want to set an elevation to the layout. If i remove the vector background then the elevation work but not otherwise. I am using the vector background to get a curved layout. So both are necessary. Please help me in this

layout_background

<vector xmlns:android="http://schemas.android.com/apk/res/android"
android:width="24dp"
android:height="24dp"
android:viewportHeight="100.0"
android:viewportWidth="200.0">
<path
    android:fillColor="#ffffff"
    android:pathData="M200,0H0v4.5h0v75.8h0c17.8,10.2 56,17.2 100.5,17.2c44.5,0 81.6,-7 99.5,-17.2h0V4.5h0V0z" />

activity_main

 <android.support.constraint.ConstraintLayout
    android:id="@+id/constraintLayout2"
    android:layout_width="match_parent"
    android:layout_height="261dp"
    android:background="@drawable/layout_background"
    android:elevation="4dp"
    app:layout_constraintHorizontal_bias="1.0"
    app:layout_constraintLeft_toLeftOf="parent"
    app:layout_constraintRight_toRightOf="parent"
    app:layout_constraintTop_toBottomOf="@+id/linearLayout"
    tools:targetApi="lollipop">
 </android.support.constraint.ConstraintLayout>