Also vbox is working when you provide height.
Code:
Ext.create('Ext.form.Panel', {
title: 'FieldContainer Example',
width: 550,
bodyPadding: 10,
items: [{
xtype: 'fieldcontainer',
fieldLabel: 'Last Three Jobs',
labelWidth: 100,
height:100,
// The body area will contain three text fields, arranged
// horizontally, separated by draggable splitters.
layout: 'vbox',
items: [{
xtype: 'textfield',
flex: 1
}, {
xtype: 'splitter'
}, {
xtype: 'textfield',
flex: 1
}, {
xtype: 'splitter'
}, {
xtype: 'textfield',
flex: 1
}]
}],
renderTo: Ext.getBody()
});