© 2019 Architectural Institute of Japan. All rights reserved. The authors have proposed effective steel connections achieving high bending stiffness and strength for timber grid-shell structures in the previous research. They are composed of joints with T-section or H-section brackets connected to glued laminated timber section members through lag-screw bolts at flanges, their bending stiffness and strength have proved to be much higher than the ones of conventional connections. However, their performance against negative out-of-plane and in-plane directions which affect the shell buckling strength are not clear yet. In this research, the bending performance of the proposed connections against negative out-of-plane and in-plane directions are confirmed through real-size mock-up tests. They are compared to the performance against positive out-of-plane. Formulas for evaluating the stiffness and strength of the connections against these directions are proposed, and their validity are verified by comparing with the test results. First, detailed analysis methods evaluating negative out-of-plane and in-plane stiffness and strength are constructed based on equilibrium of forces between steel bracket and timber beam and their compatibility condition. Next, approximating the process of neutral axis iteration, simplified formulas are demonstrated. Also, assuming the neutral axis at the center of the connections, further simplified equations for stiffness and strength are proposed. Then, real-sized mock-up specimens for the proposed connections are constructed, and simple bending tests in negative out-of-plane and in-plane directions are carried out. Their bending moment - rotational angle relationships are compared with the proposed formulas and their validity is confirmed. As results, the following conclusions are obtained. 1) TB300 (T-section bracket with 300mm length) exhibited higher bending stiffness and strength in negative out-of-plane direction than those in positive direction. TB400 (T-section with 400mm length) exhibited lower bending stiffness but higher strength in negative out-of-plane direction. 2) For in-plane bending tests, all specimens showed much lower rotational stiffness and strength than those in out-of-plane directions. Those of TB440 and HB (H-section bracket) exhibited nearly twice than those of TB300, which is caused by the effects of shear resistance of lag-screw bolts. 3) Comparing with the test results, the proposed detailed analysis methods well evaluate bending moment - rotational angle relationship, while the ultimate strengths are a little overestimated. In addition, proposed simple formulas estimate the test results in safer sides, and considered as valid for practical use. 4) TB300 has higher rotational stiffness and strength in negative out-of-plane direction than the ones in positive out-ofplane direction. However, TB440 has lower rotational stiffness and higher strength in negative out-of-plane direction than the ones in positive out-of-plane direction. As for in-plane rotational stiffness and strength, they are lower than the ones in out-ofplane direction. Therefore, the difference of rotational stiffness in out-of-plane/in-plane directions has to be considered when evaluating buckling strength of timber grid-shell structures.