bulk httpd process increase load average

Need help regarding server Load.

Facing a lot of httpd request in just 10 to 20 seconds and server load average is increase to 115.148.127 and it looks like apache crash or server httpd process is too busy.

I have already applied mod security rules and csf firewall syn flood attack on server but not able to find out permanent solution. How can I get which file is being targeted on run time which take so much load on server.