From the short animation, you will find out that Tacticals are lurking waiting for Kane nearby (one of them killed Voss earlier). Take cover and start fighting. As soon as first enemy will fall, you'll have the chance to get the Railgun.
Take care of remaining opponents and go into the complex. Open the hatch with the button (#105) and walk ahead. Get rid of the next defenders and use the elevator (#106). After going through the door, you'll have to go to the other side of the bridge, in the opportune moment getting down (route's ending is breaking under weight of one of the pylons). You'll be all the time under Harvester's fire (#107), but thanks to acceleration which is given to you by being the Strogg, you should avoid fire without any problem.
Walk ahead all the time until you'll come across three elevator's panes (#108). At present, only the one in the center is operating. Push the button and wait for the lift patiently. When you go down, move in advance the only available way, eliminating everything that moves.
In the chamber with the staircase (#109), gunfire with Tactical soldiers and Gunners awaits you. It's good to dump barrels down and then fire a few grenades towards the enemy. If you lack of shells, you'll be forced to use conventional weapons, e.g. Railgun (it has perfect optical sight).
After long walk, you'll fins yourself in the hall with the huge bulk (#110). Right behind it, there're two staircases. Take both of them and push the buttons at their ends (#111). When "heart" will deactivate, repair robots will appear round it. Approach the bulk and jump down into open passage. After going into the pipe (#112), you'll finish this level.