div id=sidebar class=col-md-4 div class=card-big div class=card-body div id=publish img alt= src=stapiclogojpg class=img-responsive

To optimize the Bootstrap code in the given HTML, you can make the following improvements:

1. Remove unnecessary classes: Remove the "card-big" class from the outermost div element, as it is not a Bootstrap class and seems unnecessary.

2. Simplify the structure: Remove the unnecessary nested div elements to simplify the code. For example, you can remove the "card-body" div if it doesn't serve any specific purpose.

3. Use Bootstrap classes for responsiveness: Instead of adding a custom class "col-md-4" to the sidebar div, you can use the Bootstrap class "col-md-4" directly.

4. Use Bootstrap image class: Replace the custom class "img-responsive" with the Bootstrap class "img-fluid" for responsive images.

After applying these optimizations, the updated code will look like this:

<div id="sidebar" class="col-md-4">
    <img alt="" src="sta/pic/logo.jpg" class="img-fluid">
    <div id="office" class="side-box">
        <div class="clearfix" id="office-title-wrap">
            <h3 id="office-title">站长最新公众号文章</h3>
        </div>
        <div class="iframe-container">
            <iframe src="paper!index"></iframe>
        </div>
    </div>
</div>

By simplifying the code and using Bootstrap classes, you can optimize the HTML structure and improve the overall performance of the page.