Not that I'm aware of - the best solution would be polling netstat or looking at server-status, however this is not very convenient for historical data.

If you've only got the standard log files, then there's not a lot of information there either (unless your site is always very, very, VERY slow) but you could at least try to calculate an estimate of concurrent connections. You'd need to sort the file by %t then go through each record working out the overlap. It's not a trivial bit of code.

A simpler approach you could simply look at the number of hits per hour multiply by the average response time then divide by the number of seconds in an hour. Of course this assumes that all requests are evenly spaced out - but you could work out a scaling factor (by measuring the current number of connections as described above). But of course if you're only recording %T (rather than %D), then the rounding will destroy any sort of accuracy in your estimate (again unless your site is horrendously slow).