Five specimens are constructed for each type of connections. Symmetrical behavior is not expected in two opposite directions. Two of the specimens from each group are tested under monotonic loading, while others are tested under reversed cyclic loading. The specimens marked with ‘‘R-’’ indicates the improved specimens for which some features are modified and/or enhanced depending on the results of the preliminary tests. Tags of the specimens, some descriptions about the loading type and the governing internal forces are presented in Table   1.

In the industrial type connection, columns are continuous hav- ing a small gap at the level of slab. The beams to be installed in lon- gitudinal and transverse directions are welded to the steel plates placed on top of the corbels and supplementary reinforcements, which will be active for negative moment, are inserted into the joint. The gap in the column, void portion of the beam and topping are filled by normal-strength concrete in the construction site, see Fig. 2a, Karadogan et al. [19].

In the residential type connection, a cylindrical pipe and four large diameter bars extending out from the lower column are inserted into the holes formed in the bottom part of the upper col- umn. After installation, these holes are grouted. The semi-cast beams with upper and lower longitudinal reinforcements are posi- tioned in the connection. The connection, void portion of the beam and topping are filled by normal-strength concrete in the construc- tion site, see Fig. 2b. In point of fact two columns and one beam are connected each other in the construction site.

Three different types of reinforcements are used during produc- tion of the specimens. The first is the regular rebars used for flex- ural and shear reinforcement. According to the tensile tests performed prior to the experiments, yield strength of the regular rebars is 419 MPa for the industrial type connections, and varies between 489 and 538 MPa for the residential type connections. Wire mesh is used as the slab flexural reinforcement with yield strength of 587 MPa. The pre-stressing tendons, which are used in beam of the industrial type connections have 4.5 mm diameter and 1400 MPa yield strength.

Concrete compressive strength determined from the compres- sion  tests  of  150 × 300 mm  cylinders  at  28 days  are  30  and 32 MPa for the industrial and residential type connections, respec- tively. The obtained compressive strengths are assessed as normal-strength. Hence, this research explains the behavior of joints made of normal-strength concrete.

2.1. Industrial type connection

The geometry of the tested preliminary specimens and some associated reinforcing details are presented in Fig. 3. Two pre-stressing tendons are existing in the beam cross section as well as the ordinary longitudinal rebar shown in Fig. 3. The lower and upper columns are cast together leaving a void at the middle part where fork type longitudinal reinforcements of semi-cast girder with protruded stirrups are placed  later  in  two  layers. The built-in steel plate at bottom face of the girder is welded to steel plate placed on the corbel of the lower column. The construction stages of the specimens are illustrated in Fig.    4.

Two short and relatively weak transverse beams are also con- structed to better represent the confinement effect provided    by these beams in the  connection. The  thickness of  hollow core  slab is 10 cm. After having placed the  hollow  core  slab  elements on the main girder, wire mesh is placed on top. Finally, 3.5 cm thick topping concrete is placed on the   slab.

ITMNM, ITMPM and ITC are identical specimens. In the first stage, their behaviors for the monotonic and cyclic loading are experimentally observed and evaluated. Subsequently, some minor need of improvements in detailing are comprehended. They are as follows: